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Managing the information that drives the enterprise
STORAGE
,
Solid-State
StorageImplementationChoicesUsing flash in storage requires you tomake choices, such as primary storagevs. performance cache, storage arrayvs. PCIe card and MLC vs. SLC.
ESSENTIAL GUIDE TO
INSIDE
Solid-state storage for the 21st century
Making a case for SSDs
Solid-state case studies
Pros and cons: MLC vs. SLC
MLC for the enterprise
SSD makes inroads with SMBs
SSD in a cache appliance
SSDs
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Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
2
oUR RESEARCH SHOWS that deployments of solid-state storage devices have morethan doubled in the year and a half weve been tracking this technology.Today, we see that more than 16% of companies have taken the plungean impressive figure when you consider that enterprise-grade solid-statehas been widely available for only a few years and the cost of NAND flashis still approximately 10 or more times that of traditional disk media.And that may just be the tip of the iceberg, as another 11% of respon-
dent firms say theyll implement solid-state this year, while one-third plan
to evaluate it. All told, only 40% of organizations dont have any plans to
move on solid-state storage in the immediate future.
As you probably knowor will
learn in the following pagessolid-
state storage comes in a variety offorms for servers, arrays or special-
ized appliances. At this point in its
evolution, approximately 75% of
solid-state users are opting to use
flash storage in a SAS or SATA form
factor that plugs right into a tradi-
tional data storage array. Still, nearly
one-third of surveyed companies are
tapping into solid-state directly at
the server, in the form of storage
devices that neatly slot into a servers PCI Express (PCIe) bus.
So why is relatively untested, extremely expensive storage so popular?
Users with the need for speed will tell you theres nothing comparable to
solid-state storage available today. It runs circles around hard disk drives
but uses a fraction of the power spinning disks require while barely warm-
ing the air around it.
Solid-state: Storage
for the 21st centuryMore and more companies are adding solid-state technologiesto their storage environments. Costs have dropped
significantly, but selective implementationsare still the most common.
Copyright 2012, TechTarget. No part of this publication may be transmitted or reproduced in any form, or by any means, without permission in wrfrom the publisher. For permissions or reprint information, please contact Mike Kelly, VP and Group Publisher (mkelly@techtarget.com).
editorial | rich castagna
Solid-state storageruns circles aroundhard disk drives butuses a fraction of thepower spinning disksrequire while barelywarming the airaround it.
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Because its still something of a luxury item for most data storage
shops budgets, users have found very specific use cases for solid-statestorage, reserving it for only the most critical IOPS-hungry applications.
The need to be selective when using solid-state has also spawned (or at
least stimulated) the development of automated techniques to move data
and apps in and out of solid-state storage as needed. Those dynamic tiering
apps are rapidly finding their way into storage systems whether or not
they include solid-state components.
Besides the choice of where to deploy solid-state, youll have to make
other decisions, such as whether to opt for single-level cell (SLC) or multi-
level cell (MLC) NAND flash, the enhanced version of MLC called eMLC (where
the e stands for enterprise) or even the much costlier non-volatile randomaccess memory (NVRAM).
All these issues and decision points are covered in this guide. Read it,
and youll be one step closer to 21st century storage.2
Rich Castagna (rcastagna@storagemagazine.com) is editorial director of the Storage
Media Group.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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MAKING A
CASE FOR
SSDsInterest in solid-state storage is
high, and with a variety of solid-
state implementations available
and newer technologies emerging,
its time to take a serious look at
how solid-state could enhance
your storage environment.
By Dennis Martin
dATA STORAGE PROFESSIONALS considering solid-state storage have myriad solid-
state storage architectures to consider, including systems that use solid-
state drives (SSDs) in various form factors, caching implementations and
appliances. If thats not enough to ponder, those planning on implementing
these systems need to decide whether to use a product that mixes solid-
state storage and traditional disk drives or to use SSD-only storage
subsystems.
But perhaps more important than just choosing the hardware, enterprises
need to decide what data to put on solid-state storage or consider some
form of software automation to move the data onto solid-state storage to
make the most efficient use of what is still an expensive resource. Deciding
what data to place on solid-state storage and how to put it there makes
choosing a solid-state storage option more complex, and your selections
will have a long-term impact.
SSDs
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SOLID-STATE-ONLY SHOPS: NOT SO SOON
In a few decades, some form of solid-state storage may be the dominantand possibly only form of enterprise data storage. But given the present
state of matters, that day is (at best) on the distant horizon. We might
dream of replacing all our electro-mechanical disk drives with solid-state
storage if cost werent a factor, but theres nowhere near enough semicon-
ductor fabrication production capacity available today to satisfy the total
storage capacity thats deployed in IT shops.
But there are some promising
signs. Enterprise solid-state storage
prices are dropping relative to enter-
prise hard disk drives (HDDs). Notthat long ago, enterprise solid-state
storage was as much as 40 times
the price of an equivalent capacity
of enterprise hard disk drive storage.
The price comparison ratios are in
the neighborhood of 25% to 50% of
that today, depending on specific
solid-state storage products.
As a result of this pricing and capacity disparity, data storage managers
and administrators are finding that solid-state storage complements existing
traditional forms of storage. Theyve deployed, or are planning to deploy, solid-
state storage where high performance, low latency or energy savings are
needed.
There are two basic ways to implement solid-state storage technology:
Use solid-state storage directly as a primary store
Use solid-state storage as a cache in front of spinning disks
Each of these implementations has its advantages and disadvantages,
and implementations vary among storage vendors. And some vendors offer
one implementation now while planning to offer the other.
USING SOLID-STATE FOR PRIMARY STORAGEFor vendors that implement solid-state storage directly as a primary data
store, many use the standard disk drive form factor. This implementation
method is simple to understand and is compatible with current subsystem
designs and configuration processes. The one downside to this approach is
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
5
Not that long ago,
enterprise solid-statestorage was as muchas 40 times the priceof an equivalentcapacity of enterprisehard disk drive storage.
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that many of todays controllers and subsystems werent designed for disk
drives with an order of magnitude of faster performance at the drive level,so vendors typically dont support a large system completely full of solid-
state disk drives. But this is changing as vendors design and build improved
controllers that can handle many more solid-state drives. The good news is
that significant performance gains can be achieved with a relatively small
number of SSDs, often only one full or partial drive shelf. Some users are
reporting five to eight times performance gains for some workloads with
a relatively small amount of solid-state storage.
Were also seeing an increasing number of solid-state-only storage
products available today and planned for release over the next several
months. These systems are designed to use solid-state storage as theprimary store, with capacities in the single- or double-digit terabytes
today and larger capacities coming soon.
For users who have implemented solid-state storage as a primary store,
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
6
Form factors and interfaces
sOLID-STATE STORAGE comes in a variety of form factors, including nearly
all the disk drive form factors, as internal modules within a storage
system or as a PCI Express (PCIe) bus card. The PCIe bus form factor
provides the potential for very high bandwidth storage access within
a server or workstation.
Enterprise solid-state drives are available in 2.5-inch and 3.5-inch
drive form factors that are compatible with todays servers and storage
systems. The primary interfaces for these are SATA, SAS and Fibre
Channel (FC). The SATA interface is available for many solid-state
drives, especially for the consumer and desktop market. FC has a
long future as a SAN interface but is approaching end-of-life as a
disk drive interface. Disk drive suppliers and solid-state storage sup-
pliers are moving away from FC as a drive interface in favor of 6 Gbps
SAS as an enterprise drive interface. We expect the FC interface on
3.5-inch drives to stick around for a while to maintain spare parts on
the relatively large number of 3.5-inch FC drives in enterprise disk
subsystems. And we anticipate that relatively few 2.5-inch enterprise
drives will have a FC interface.
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the big question focuses on what data to put on the solid-state storage.
There are some obvious candidates, such as database indexes, heavilyaccessed database tables, temporary scratch areas, log files or any other
hot spot. However, this is often not a static solution. Some data thats hot
today may not be hot tomorrow. So storage administrators, database admin-
istrators or other IT technicians may have to continually monitor data usage
patterns and be prepared to make adjustments on a fairly regular basis. In
some cases, this increased management burden may be too much work
and involve too much operational expense to be worth the tradeoff for
increased I/O performance.
The answer is to provide an auto-
mated way for the storage systemto identify the hot data, move it onto
the solid-state storage automatically
and to then move it to slower stor-
age when it no longer requires solid-
state performance. Many vendors
provide forms of tiering software
that does exactly that. This software
observes the I/O patterns for a time
and then moves the data in a way
thats transparent to the host appli-
cations. Many of these automated
solutions allow the administrator to
determine what activity level defines
hot data, set the time period over
which the observations are made
and then set a separate parameter
that controls the frequency of data movement (anywhere from hourly to
weekly). Some of this software has the ability to make recommendations
about the data tiering based on the observations it has made, such as rec-
ommending a 10%/90% mix of solid-state vs. spinning disk.
Solid-state-only storage products eliminate the need to move data from
faster to slower storage because all the data is on fast storage. These sys-
tems appeal to customers who want to put an entire application and its
data on solid-state storage. At todays price points, these solutions tend to
be deployed for critical applications only. The decision (and budget) to acquire
them tends to come from line-of-business owners or architects rather than
from the IT department.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
7
The answer is toprovide an automatedway for the storagesystem to identify thehot data, move it ontothe solid-state storageautomatically and
to then move it toslower storagewhen it no longerrequires solid-stateperformance.
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CACHING WITH SOLID-STATE
The other basic implementation is to use solid-state storage as a cache infront of spinning disks. This method has the advantage of always acceler-
ating the hot data in real-time, since only the hot data is likely to be in cache.
And because the solid-state storage is acting as a cache, theres no need
for an administrator to decide what data should be placed on it. The basic
questions here are what size cache is appropriate and which workloads
should be directed toward the cache to make the best use of the solid-
state device.
Solid-state caching solutions can be built into existing storage systems or
servers, or delivered as external appliances. Adding flash memory as a
cache inside a storage subsystem in effect provides a level 2 cache notunlike the L2 cache found on many processors inside todays computers.
This added cache capacity improves
performance for most if not all oper-
ations. In addition, because flash
memory is nonvolatile, this cache
provides some extra protection in the
event of power loss. But issues such
as cache coherency, and whether
the cache is DRAM-based or flash
memory-based, remain. Generally,
a cache is tied to one processor or
controller, and there are various
cache management functions that
can be applied to allow caches to
work properly with multiple proces-
sors or controllers. In addition, stor-
age systems that use caching can add special features to their internal
OSes that are aware of the cache and can provide additional flexibility,
such as the ability to assign different I/O priorities for I/O going to different
volumes on the storage system.
The caching appliances add the benefits of cache without requiring
changes to any existing servers or storage systems. These appliances fit
easily into the storage network and can accelerate all I/O going through
them, even sending data to different storage subsystems at the same time.
Many of the appliances can be set to write-back, write-through or pass-
through for any given volume they accelerate. Some of the caching appli-
ances are constructed in such a way as to allow their memory modules
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
8
Adding flash memoryas a cache inside astorage subsystemin effect provides a
level 2 cache notunlike the L2 cachefound on manyprocessors insidetodays computers.
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to be hot-plugged, so maintenance or growth can occur without taking down
the entire appliance.The big question for a caching implementation is how much cache is
enough. For many workloads and applications, a relatively small amount of
cache (5% to 20%) relative to the total storage allocated to that application
is enough to provide significant performance improvements. For other
workloads, the cache needs to be large enough to hold the entire volume
to achieve appreciable performance gains.
ITS ALL ABOUT PERFORMANCE
Solid-state storage, however its deployed, offers the promise of significantperformance gains. Weve seen results of seven to nine times overall per-
formance gains in our lab testing for various real-world applications (email,
database, etc.) when configured optimally for the application.
With performance gains of that magnitude possible, whats not to like?
Certainly, pricing is a factor. However, consider some of the current methods
that are used to increase performance of spinning disk drives, such as
short stroking. This technique spreads data over many disk drives by
using only a portion of the capacity of each drive for data so as many
spindles as possible can be applied to improve performance. To achieve
desired performance goals, some users short stroke some of their enter-
prise disk drives using ratios of 7-to-1, 8-to-1 or 9-to-1, which means
theyre using only 1/7th, 1/8th or 1/9th of the available capacity on each
drive. If the price of an enterprise SSD is 10 times to 15 times the price of
the spinning drives being short stroked, it may make sense to move that
application data to enterprise SSDs and get the required performance
while using much less power and space.
Almost all data storage system vendors now offer configurations that
use a combination of solid-state storage and enterprise SATA storage
instead of arrays full of enterprise spinning disk drives. These new config-
urations typically offer higher performance, equivalent capacity, lower
power consumption, smaller space requirements and lower total hard-
ware costs. 2
Dennis Martin has been working in the IT industry since 1980. He is the founder and
president of Demartek, a computer industry analyst organization and testing lab.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
9
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Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
10
IT SHOPS THAT implement solid-state storage technology must decide whether
to use it in traditional disk arrays, as cache, in appliances or in servers.
Application needs generally determine the solid-state storage choice
that will bring the greatest performance boost. Types of I/O-intensive apps
that tend to benefit from solid-state storage technology include database,
data warehouse, data mining, analytics and Web serving.
If the I/O bottleneck is isolated to a single server or application, server-
based solid-state storage might be the best approach, whether thats with
2.5-inch or 3.5-inch solid-state drives (SSDs), PCI Express (PCIe) cards ordual in-line memory modules (DIMMs).
An IT shop with data sets that are intermittently hot might select NAND
flash cache, in which the system typically determines the hottest data to
accelerate.
If an IT shop has several I/O-intensive applications that need a perform-
ance boost, it might opt for SSDs in a shared storage array. A solid-state
appliance or solid-state-only array is another option when an IT shop wants
to isolate the data to a single device.
App needsdictate whereto use solid-state storageSolid-state storage technology can be used in different
ways. IT must decide whether to use technology in disk
arrays, as cache, in appliances or in servers. By Carol Sliwa
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The notion of a solid-state appliance dates back to the earliest dynamic
random access memory (DRAM) systems from Texas Memory SystemsInc., which now also makes NAND flash-based products. Framingham,
Mass.-based IDC continues to track solid-state-only appliances from
Texas Memory Systems and other vendors, including Dataram Corp., Nim-
bus Data Systems Inc., Violin Memory Inc. and Whiptail Technologies Inc.
But some vendors, analysts and users prefer to call the appliances solid-
state-only arrays or dedicated solid-state storage devices.
Read on for case studies focusing on each of the solid-state storage
options, with an eye toward the decision-making process.
CASE STUDY 1SETAO: SSDs in storage arrays facilitate performance boost
for several applications
Background: The private company that operates the public transporta-
tion network for the city of Orleans, FranceSocit dExploitation pour les
Transports de lAgglomration Orlanaise (SETAO)replaced its NetApp Inc.
storage with Pillar Data Systems Inc.s Pillar Axiom disk arrays (Pillar has
since been acquired by Oracle Corp.) approximately four years ago and
began using SSDs in 2009.
SETAO manages and stores data from buses, trams, vehicle radios, video
surveillance cameras, traffic lights, billing systems and electrical systems.The company makes real-time traffic information available via mobile devices
and surveillance data to law enforcement.
Technology: At Pillars suggestion, SETAO purchased its first solid-state
drive enclosure in July 2009. The company now has 600 GB of SSDs in each
of its three Pillar arrays: an Axiom 500 that also has 100 TB of SATA disks,
an Axiom 500 with 16 TB of SATA and an Axiom 600 with 16 TB of SATA. Two
arrays are located at the primary site in Orleans; another is approximately
12 miles away.
SETAO also upgraded its servers and storage network with cutting-edge
technology. The company runs Fibre Channel over Ethernet (FCoE) betweenits servers (which are equipped with Emulex Corp. converged network
adapters, or CNAs) and Cisco Systems Inc. Nexus 5000 top-of-rack switches,
which split the 10 Gigabit Ethernet (10 GbE) and Fibre Channel (FC) traffic.
The storage traffic connects over 4 Gbps FC to Brocade 300 FC switches
and to the Pillar Axiom arrays.
SETAO uses FalconStor Software Inc.s IPStor storage virtualization tech-
nology to replicate between the arrays. The company also used IPStor to
migrate data from the NetApp systems to Pillar arrays.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
11
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Why SSDs in arrays: Olivier Parcollet, director of systems information at
SETAO, prefers SSDs in a shared storage environment because he wants to
improve the performance of several applications, some Windows based
and others Linux based.
Using solid-state storage technology in a server would have restricted
the performance boost to a single application unless he used virtual
servers. Parcollet said he isnt comfortable using SSDs in a physical server
with virtual machines (VMs) because of the risk of application loss in the
event of a server failure.
Because I have shareable storage on Fibre Channel, if I lose a server,
an application could run on another one very, very quickly, he said.
Results/Benefits: SETAO uses SSDs with four of its most important
apps. Its initial use was for the traffic simulation software that plots busand tram routes, as well as the optimal number of vehicles and drivers.
Application response time was approximately two hours on SATA disks, but
its nearly instantaneous on solid-
state drives, allowing SETAO to run
a greater number of simulations
per day, according to Parcollet.
We use three buses and seven
drivers less than the year before to
do the same work, Parcollet said,
noting that SETAOs financial team
claimed the one-year savingsamounted to approximately
1 million euros ($1.39 million USD).
SETAOs VMware Inc. virtual
desktop infrastructure (VDI) also
benefited from SSDs. Provision-
ing/booting 200 virtual desktops
took approximately 20 minutes with SATA drives, but takes only about five
seconds with SSDs, Parcollet said.
Results were similar for queries to the Oracle databases that store meta-
data about video images (which are archived on SATA disks) from 300 munic-ipal surveillance cameras installed throughout the metropolitan transportation
network. A search for a particular image, such as men wearing blue trousers
and a red hat, might have taken 30 minutes with SATA drives. The search
completes instantly with SSDs, he said.
More recently, SETAO shifted approximately 100 GB of financial data
from SATA disks to solid-state drives. Processing that once took three
hours, according to Parcollet, now finishes in about two minutes.
Greatest challenge with SSDs: Implementing SSDs wasnt especially
difficult for SETAO. The staff installed the SSD enclosure, adjusted the graph-
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
12
Provisioning/booting200 virtual desktopstook approximately20 minutes with SATA
drives, but takes onlyabout five secondswith SSDs.
OLIVIER PARCOLLET, director of
systems information, SETAO
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ical user interface and changed the LUNs quality of service (QoS) to premi-
um. Shifting to premium QoS triggered the Pillar Axiom array to automati-cally move the designated data from SATA disks to SSDs.
The greater challenge was deciding which application data to prioritize
onto solid-state drives. Parcollet had no interest in solid-state storage
technology with automatic tiering to shift the hottest data to SSDs. Auto-
tiering could put unimportant data onto the SSDs, he reasoned; he wanted
to make the application decisions himself.
Parcollet consulted Pillars built-in monitoring tools to determine the
most I/O-intensive applications, but he didnt move several applications
to SSDs at the same time, nor did he shift entire applications.
Only some parts of the applications need to be on SSD, Parcollet said. All
the data doesnt need to stay in SSDs; only the more accessed [data does].
For instance, only the control
files, indexes and redo logs of
SETAOs Oracle databases make
use of SSDs. With VDI, SETAO
stores only the gold image on
SSDs and spreads the end-user
data across SATA drives.
One VM per user consumes
only about five I/O per second,
Parcollet said. Theres no needto use SSD every time for VDI.
But SSD is good to generate
the images very, very quickly
for provisioning.
Peer advice: Parcollet recommends SSDs for small, high-transaction,
I/O-intensive applications rather than large applications. We cannot install
all applications on SSD because its very, very expensive, he said, noting
the companys SSDs cost approximately five times more than its SATA
disks. Pillars list price for a brick with 64 GB SSD drives (12 active drives,
one hot spare) is $49,000.
Parcollet cautioned that all storage features may not be available when
using solid-state drives. He said he cant use Pillars thin provisioning with
SSDs, for instance.
Addressing another potential downside of SSDs, Parcollet said hes not
worried about the drives wearing out. I asked Pillar the question when I
bought the SSD drives, and they guaranteed that the [SSD] life will be as
long as a traditional drive because theres a [memory] reserve on each
drive, he said.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
13
Theres no need touse SSD every time forVDI. But SSD is good togenerate the imagesvery, very quickly for
provisioning.OLIVIER PARCOLLET, director of
systems information, SETAO
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CASE STUDY 2Ultimate Software Group: Flash cache provides assist with
team-based application development
Background: Ultimate Software Group Inc. in Weston, Fla., provides hu-
man resource and payroll Software-as-a-Service (SaaS) to more than 2,000
customers. A 200-member development team writes and tests an average
of 21 application iterations, known as application builds, per week.
Technology: In June 2009, Ultimate Software Group purchased two
DRAM-based 16 TB performance acceleration module (PAM) cards from
NetApp. The PAM cards functioned as read caches for the organizations
pair of clustered NetApp FAS3170s, which store data from Microsoft Corp. SQL
Server databases, VMware VMs and file shares, and serve as the central
repository for the daily application builds.In 2010, Ultimate Software Group bought two of NetApps newer 512 GB
Flash Cache (PAM II) cards for the FAS3170s and moved the lower-capacity
DRAM-based PAM cards to the pair of FAS3140s that IT uses for perform-
ance, stability and reliability (PSR) testing.Why choose solid-state cache
over SSDs: It was a lot cheaper
than buying SSDs for 30 TB of
storage, said Brian Goldberg,
director of infrastructure and
deployment strategy at Ultimate
Software Group.Results/Benefits: The PAM
cards store in cache memory the
application builds that developers
request most often, and read
speeds have increased dramatically
in response, Goldberg said.
We write [the application build]
once, and then we read it many
times, which is why the PAM cards were very attractive, Goldberg said.
Instead of the filer going down the loop to get the actual data from thephysical disks, bringing it back and then sending the response to the user,
it basically goes to the cache, gets it and sends it right to the user a lot
faster.
Real-time performance monitoring showed IOPS was far lower with
the PAM cards in place. The load on the two NetApp FAS3170s, which store
more than 37 TB of data, has decreased 40% to 50% since the installation
of the DRAM-based PAM cards, Goldberg said.
Adding the new Flash Cache helped the developer team increase the
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
14
We write [the applica-tion build] once, andthen we read it manytimes, which is whythe PAM cards werevery attractive.
BRIAN GOLDBERG, director of
infrastructure and deployment
strategy, Ultimate Software Group
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number of application builds per week with no impact on performance.
Weve been growing our products and our teams and the number of
environments each team owns, he said. We knew we were going to be
deploying more and more, and we had concerns that if we kept hitting the
NetApp [FAS boxes], we would have performance problems and we would
need a bigger filer.
Greatest challenge: Goldberg said he would like to add more PAM cards,
but the cost is prohibitive. Ultimate Software Group spent close to $30,000
on its initial pair of 16 TB DRAM-based PAM cards and more than $100,000
on the second set of 512 GB Flash Cache/PAM II cards, he said.
But, he added, We definitely felt that the value weve gotten from them
is worth it.
Peer advice: I would definitely get them from the beginning, Goldberg
recommended. I wouldnt say, Oh, let me set up my filer without them,and I can always add them later. Youll definitely reap the benefits if you
start using them from Day 1.
CASE STUDY 3Solid-state-only arrays/appliances conserve space, power
for logistics company
Background: Odyssey Logistics & Technology Corp., based in Danbury,
Conn., provides managed logistics and services to the global chemical and
process manufacturing industries. Its primary data center is located inCharlotte, N.C., and its secondary data center is in Raleigh. Odyssey sup-
plies information such as carrier selection, rack scheduling, transit time,
shipment tracking and billing to customers through SaaS-based apps.
The thing thats hard to try to manage is how many electronic transac-
tions we do on the back side at any given time when you have users on the
front side, said Brad Massey, Odysseys director of IT support services. Lets
say we have major retailers in the U.S. who send us batches of 4,000 or 5,000
orders that need to be planned pretty quickly. We might be load optimizing
those shipments on the back end while we have people on our website
trying to do regular queries. We still need to offer acceptable performance.
Technology: Approximately four years ago, Odyssey Logistics & Technology
purchased Texas Memory Systems RamSan-400, a 128 GB DRAM device; six
months later, Odyssey upped the scalability with a NAND flash-based Ram-
San-500, a 2 TB NAND flash device. About a year ago, Odyssey added a 5 TB
RamSan-630 flash-only array to run its data warehouse and analytics.
All of our customers see very consistent performance because of the
solid-state arrays on the database, Massey said. Prior to that, we always
seemed to be playing catch-up with adding spindles to the storage array
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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so we could keep our database performance up to speed.
Odyssey reserves its RamSans almost exclusively for its Oracle work-
loads, running the entire databases on the RamSans. All the companys
custom-built and packaged applications rely on the Oracle data stores,
from the accounting system to the IBM WebSphere partner gateway.
Thats where we really need the throughput, Massey said. Our data-
base requires the ability to burst our I/O very quickly, for sometimes long
or short periods of time. Whether youre looking at SSD or disk-based systems,
youve got to size the systems to your peak I/O whether or not youre going
to use it all the time.
In addition to the RamSans,
Odyssey Logistics & Technology
recently purchased five 100 GB
flash drives for one of its EMCClariion CX4 arrays. One drive will
serve as a hot spare and another
for parity, leaving approximately
300 GB usable. The most likely use
case for the new SSDs will be a
VDI project.
If you have a lot of VMs boot-
ing up at the same time in a first-
of-the-morning scenario, you can
create an I/O storm, Massey noted.
You really need your golden
images to be pulled from very
quickly.
Why solid-state-only array/appliance: Odyssey doesnt own its data
centers; it operates at colocation facilities. So, energy-efficient, space-
saving solid-state appliances hold extra cost-saving appeal over traditional
disk arrays.
When you look at a RamSan device and the amount of I/O theyre able
to pack in a 3U device, as opposed to all of the disk enclosures and the
spinning disks you would have to have to get for the same amount of
IOPS, Massey said, its really a compelling story.Server-based storage doesnt factor into Odysseys long-term plans.
Odyssey Logistics & Technology runs Cisco Unified Computing System
(UCS) diskless servers. Most of our configurations at the data center run
boot from SAN, so we typically eliminate all of the disks out of servers
where we can, Massey said.
Results/Benefits: Waits of eight to 10 seconds on webpage refreshes,
and occasional response times as high as 30 seconds under especially
heavy loads, dropped to subsecond times for most queries with the shift
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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If you have a lot ofVMs booting up at thesame time in a first-of-the-morning scenario,you can create an I/Ostorm. You really needyour golden images tobe pulled from veryquickly.
BRAD MASSEY, director of IT support
services, Odyssey Logistics & Technology
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from hard disk drives to solid-state storage, according to Massey.
DRAM-based devices tend to work better than flash at writes; the flash
works fine for reads, noted Eric Brown, a database administrator at Odyssey.
We have an extremely high read-only environment, Massey added. If
our profile was heavy write, we would certainly make different decisions.
Odyssey used to refresh its data warehouse only periodically through-
out the day, but with the RamSans, its able to crunch much of the data in
real-time for customers accessing its Web dashboards.
Peer advice: Massey recommends IT shops consider solid-state drives
where they need optimal performance. He also urged them to factor in
space and power requirements when comparing the acquisition cost of
traditional disk-based storage arrays and solid-state storage technology. 2
Carol Sliwa is a senior writer in the Storage Media Group.Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
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Making aase for SSDs
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os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
18
SOLID-STATE DRIVES (SSDs) may now be affordable enough to merit serious
consideration when planning a storage system.
If youre thinking of buying SSDs based on flash memory technology,
its worth learning about the differences between multi-level cell (MLC)
and single-level cell (SLC) flash.
MLC vs. SLC:Which flash SSD is right for you?
The type of flash SSD you choose depends on the
performance you need and the price you want to pay, but the
differences arent as great as you may think. By Manek Dubas
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As with any technology, there are tradeoffs, depending on which of the
two types of flash SSD you select. MLC flash is the most common and isoften found in consumer-grade products such as cameras, phones, USB
memory sticks and portable music players, but its also present in some
enterprise storage products.
The main characteristic of MLC
flash is its low price, but it suffers
from higher wear rates and lower
write performance compared with
SLC technology. SLC is faster and
much more reliablebut also more
expensiveand is featured in the
best-performing storage arrays.
In practice, however, the differ-
ences arent quite as clear as you
might expect. To see how this technology is developing, its application
and where its heading, we need to look at how the two types of flash
memory work and how theyre sold.
But storage sales discussions arent normally about the tradeoffs of
MLC vs. SLC, according to Valdis Filks, research director for storage tech-
nologies and strategies at Gartner Inc. This is normally hidden by imple-
mentation, he said. In other words, its up to the enclosure manufacturer
of the storage array, and its the controller thats more important than theunderlying storage technology.
MLC vs. SLC HEAD TO HEADVendors may prefer not to discuss the differences between the technologies,
but understanding the underlying technology can influence deployment
strategies. So, what are the key differences between MLC and SLC flash
SSDs?
All flash memory suffers from wear, which occurs because erasing or
programming a cell subjects it to wear due to the voltage applied. Each
time this happens, a charge is trapped in the transistors gate dielectric
and causes a permanent shift in the cells characteristics, which, after a
number of cycles, manifests as a failed cell.
SLC uses a single cell to store one bit of data. MLC memory is more
complex and can interpret four digital states from a signal stored in a
single cell. This makes it denser for a given area and so is cheaper to
produce, but it wears out faster.
An MLC cell is typically rated at 10,000 erase/write cycles, while an SLC
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
19
SLC is faster andmuch more reliablebut also more expen-siveand is featured
in the best-perform-ing storage arrays.
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cell might last 10 times that before failing. However, manufacturers of
products consisting of MLC cells can and do have ameliorating technologiesand techniques at their disposal.
According to Andrew Buss, service director at analyst firm Freeform
Dynamics Ltd., amelioration techniques used by most vendors include wear
leveling, which moves write cycles around the chip so cells wear evenly;
on-device deduplication, which reduces the volumes of data written and
so lowers wear; redundancy, which reserves a portion of the devices
capacity to replace cells as they fail; and write optimization, which stores
data writes so they can be made into large chunks to reduce the number
of write operations. The emerging term for MLC products that incorporate
such techniques is enterprise MLC (EMLC).
Most such techniques are implemented in the device controllerthe
interface between device and computerwith companies such as Sand-
Force Inc. and Intel Corp. among the most advanced in implementing such
techniques, according to Buss. And despite the endurance issues related
to SSDs, vendors say they remain more reliable than spinning media.
USE CASESAccording to Gartners Filks, the
implementation determines the
technology. So applications suchas high-speed databases, whose
performance is measured in terms
of transactions per second, should
be matched to the appropriate tech-
nology selected on the basis of price/
performance.
Its about serving more customers in a given time. Thats what SSD
vendors talk about, Filks said.
Despite this, MLC and SLC tend to be used for different applications due
largely to the four-fold price difference per gigabyte between them. As we
have seen, MLC can be found in consumer-grade products and in the enter-
prise where performance, while important, isnt the primary consideration.
When used in the same storage system, the two types of SSD can be
tiered in the same way as tiering with spinning media; most storage
product vendors include a form of automated SSD tiering, Freeform
Dynamics Buss said. SLC typically tops the storage tier tree in financial
services organizations, where high-speed access to large databases is
essential and price is a secondary issue. Buss said he believes future
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
20
Its about servingmore customers ina given time. Thatswhat SSD vendorstalk about.VALDIS FILKS, research director for storage
technologies and strategies, Gartner
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products will increasingly be integrated with both flash SSD types and
spinning media in performance/cost-based tiers.Most enterprise applications will rely on a form of database and so
will need SSDs. An example is content management systems, where an
end user is waiting for things to happen; also Exchange servers, websites,
media storageall of which you can use MLC for, Buss said. However,
you still need to do due diligence and buy appropriately. There are new
solutions coming along to make MLC better.
End-user Roger Bearpark, assistant head of information and communi-
cations technology (ICT) at the London borough of Hillingdon, has installed
520 GB of MLC-based SSD-based storage into his Compellent arrays. MLC
is poorer on endurance and performance, but is up to three or four [times]
better on price, he said. We got a phenomenal rate of return on investment
by putting small amounts of active data on SSD, which produced a 13-fold
improvement in access times.
FUTURESAccording to Gartners Filks, SSDs wont replace spinning disks. Everyone
says SSDs will replace disks, maybe in about 15 to 20 years time, but as
SSD prices drop, so do those of disks, he said. And SSD prices will never
fall as far as disk because factories cant make enough. It means only the
working data set needs to be on SSD, and thats about 5% to 15% of thetotal.
However, Filks predicted that SSDs could eventually replace tape as a
deep archive technology because it offers similar benefitsnonvolatility
and zero power usage when not in usealthough he predicted this will
take 10 years to 20 years.
As prices fall and reliability techniques improve, it seems likely that MLC
technologys price advantage will keep it ahead of SLC for all but the most
demanding of applications, as it remains significantly faster and more robust
than spinning media. 2
Manek Dubash is a UK-based freelance journalist.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
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OLID-STATE STORAGE is being adopted in the enterprise but
not at the pace that many observers originally predicted.
While there are a variety of reasons for this, one that cant
be ignored is the cost. Solid-state storagewhich, for the
enterprise, is typically based on single-level cell (SLC)
flashis expensive. In many cases, if your IT shop does
not have a specific application performance problem
thats impacting corporate revenue, youre not likely to buy
SLC-based solid-state storage. There are many applicationsthat could benefit from the solid-state performance boost,
but for most of them, that boost hasnt yet been shown to
be worth the investment.
But multi-level cell (MLC) flash in enterprise arrays may be just the
solution you need to make the solid-state jump. MLC flash is cheaper than
SLC, making solid-state technology more appealing for a broader set of
applications, perhaps those that could benefit from a measurable but not
massive jump in performance.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
22
Using
MLC flashmemory in
enterprise arraysFind out how enterprise MLC flash can bethe right solid-state storage option for ITorganizations looking for a measurable
increase in performance without the costof SLC-based flash. By George Crump
s
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WHAT IS MLC FLASH?
Solid-state flash drives are made up of memory cells. Traditionally, withSLC memory, those cells are written to once per segment of data. MLC
flash, on the other hand, writes two data segments to the same cell, effec-
tively doubling the capacity of the flash storage. However, this method
means MLC storage has lower performance and reliability than SLC memory.
MLC flash is also likely to wear out faster than SLC because flash storage
can handle only so many write cycles per cell. As a result, MLC flash storage
has been relegated to consumer devices like laptops and phones. But sig-
nificant improvements have been made in both the understanding of MLC
and in the technology that surrounds it, and some suppliers are now pro-
posing its use in the enterprise.
PROTECTING MLC FLASH STORAGEWhile its true that MLC will fail more often than SLC flash, advancements
in intelligence around MLC and how its protected are changing the dynamics.
First, MLC production processes have improved; some suppliers now offer
eMLC (enterprise MLC) with write
cycles as high as six times that of
standard MLC (30,000 vs. 5,000). Sec-
ond, the process of writing data to
the cells has improved such that nosingle cell of the flash disk becomes
hot; wear leveling ensures writes are
spread evenly across the available
cells. Third, most if not all eMLC
systems have spare unreported
capacity, so if a cell does wear out,
its data can be written to a new drive
and cell. Besides these special con-
siderations around the flash memory
itself, its important to remember that in many cases this memory will be
installed in an enterprise-class storage system, so technologies like RAID
and mirroring can be used to provide further protection from failure.
MLC FLASH MEMORY PERFORMANCE ISSUESNow lets talk about the performance concerns around MLC. While MLC isnt
as fast as SLC, it is faster than a single 15,000 rpm drive in both read and
write operations. Many data centers are looking for a measurable but cost-
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
23
While its true thatMLC will fail more
often than SLC flash,advancements inintelligence aroundMLC and how its pro-tected are changingthe dynamics.
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correct performance boost. SLC flash may be overkill whereas MLC may be
just right.The big limiter in the performance of MLC, or that of any flash-based
solid-state drive (SSD), is when the drive reaches whats called steady state.
This is when the drive has been completely filled up for the first time and
there are no more empty cells to put data into. From that point forward, any
new data the flash controller needs to write must be written to cells that
have no in-use data on them. The not-in-use data is erasedwhich in the
flash world means the cell is written to with zerosand then the new data
is written to the cell. Obviously, these two steady-state writes take time;
factor in the parity writing in a RAID algorithm and the performance gets
worse. And this write cycle can deliver erratic and unpredictable I/O per-
formance, especially when the system is busy with a lot of write traffic
and is near capacity.
To combat this problem, most flash controllers now have the ability
to do something called garbage collection. During idle times the flash
controller will scan the drive looking for cells that store data marked as
removable by the operating system (typically a delete command) and per-
form the erase write ahead of time. Garbage collection is more important
in MLC or eMLC-based systems be-
cause theyre slower at processing
a write cycle (more data per cell), so
having those cells cleaned out aheadof time is critical. Another technique
storage systems use is preserving
some flash memory as unallocated.
For example, if 20% is left in reserve,
in most cases the write cycle wouldnt
have to be performed while data is
written to the drive. The flash con-
troller will use the spare cells.
MLC flash makes sense for IT
shops that have applications where performance needs to be improved
but not to an extreme level. Theres enough technology and redundancy
surrounding these systems that they can be implemented with confidence
into many environments without the risk of data loss. 2
George Crump is founder and president of analyst firm Storage Switzerland.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
24
MLC flash makes
sense for IT shopsthat have applicationswhere performanceneeds to be improvedbut not to an extremelevel.
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d
SSD technologymaking inroads with SMBsAmong users, solid-state is gaining ground as a sensibleoption to protect against data loss and to reduce power
consumption. As a result, companies of all sizes are
evaluating the technology. By Alan Earls
STORAGE Essential Guide to Solid-State Storage Implementation Choices
ESPITE relatively high costs, solid-
state drive (SSD) technology is
continuing to attract new users,according to a survey of more than 500
businesses conducted earlier this year.
The survey, conducted by Kroll Ontrack, indicated that
nearly 70% of respondents use solid-state or flash technology, or
at least have plans to implement the technology in the near future.
Approximately 75% of respondents indicated they believed SSD tech-
nology delivered higher performance than spinning disk drives. They also
reported a perception that solid-state is a safer medium to protect against
data loss and that it consumes less power, and is therefore more environ-
mentally friendly.Some of those issues were on the mind of Les Barnes, a
senior vice president of information technology at Bank
of Fayetteville in Arkansas, when he faced a SQL
Server performance problem.
Our two biggest applications are
check imaging and our system
that manages merchant
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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processing. They were both SQL Server based and both had developed an
annoying habit of pausing frequently, causing consternation for users
and slowing the flow of work, Barnes said.Barnes said he suspected part of the problem was related to slow
I/O response as a consequence of disk access time. So approximately 14
months ago, he installed Dell Inc.s EqualLogic storage products, including
the PS6000XVS, a hybrid storage array that includes both 15K SAS drives
and SSDs. He said the implementation of SSD technology was an element
in a broader effort to implement tiered storage, since the XVS system
incorporated both SAS drives and higher speed SSDs.
The problem disappeared as soon
as the applications had access to the
SSDs, Barnes said. Now, he said, withthe SSDs in place, database latency
has dropped from the low single
digits to less than a millisecond.
According to analysts, Barnes
is far from alone in finding solace
for storage troubles in solid-state
storage adoption.
Vendors from the smallest start-
ups to the largest IT vendors are
getting in the game, said David Hill,an analyst at Mesabi Group LLC.
Solutions are being touted at the
array level, the network level, at the
host level or even as DAS [direct-
attached storage].
The reason is simple, according
to Hill. SSD technology promises to
eliminate poor application performance that can arise because of I/O
bottlenecks, such as the performance gap between server speeds and
hard disk drive (HDD) speed, or as an unintended consequence of a highlevel of server virtualization.
Hill said theres still a question of how much of a monetary value can
be tied to that performance improvement. If increased revenue (and con-
sequently profit) exceed the added cost and management of SSDs, then
solid-state drives would be a good fit.
He said SSDs may also be able to offer other improvements, such as
being able to speed backup jobs that need to be done within a particular
time window.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
26
Vendors from thesmallest startups tothe largest IT vendorsare getting in thegame. Solutions arebeing touted at thearray level, the
network level, at thehost level or even asDAS [direct-attachedstorage].
DAVID HILL, analyst, Mesabi Group LLC
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That could result in extra cost, but the business may be able to justify
it. In addition, there may be some cost tradeoffs, Hill said. UnderutilizedHDDs that SSDs render unnecessary for performance purposes may be
repurposed for other tasks, and thus defer the need to purchase more
disk storage for a time.
Over a period of years, Hill said, SSDs will displace most if not all high-
performance SAS and Fibre Channel (FC) drives, but not capacity-oriented
SATA drives.
If theres a performance issue, then SSDs can be evaluated as a solu-
tion, he said, regardless of company size. For instance, a large enterprise
may not have application performance issues, but a small- and medium-
sized business (SMB) may be dependent upon an application that criesout for greater performance, Hill said.
The problem, and not the size of the company, is the determinant, Hill
said. On the other hand, smaller companies may not have the resources
to evaluate all the SSD solutions properly when compared to companies
that have a larger IT staff, he noted.
Mark Peters, an analyst at Enterprise Strategy Group, said theres no
defining characteristic of the typical user or use case with SSD technology.
Some SMBs may literally put everything on solid-state in the server,
while others are specing a limited amount of turbo boost in their stor-
age subsystems, he said.Peters also said the economics of using SSDs arent as scary as many
think because organizations have had to use more spinning disk re-
sources to achieve performance goals that may be within easy reach of
lower-capacity SSDs.
Its still a small market when measured in revenue and terabyte pen-
etration terms, but its impact is about IOPS and performance rather than
capacity, he said. Id go so far as to say that every storage systems
vendor has an offering, and often multiple ones. And the use case range
is essentially as a storage tier [persistent data] or for solid-state to be
used as a cache.
Peters said the adoption of SSD technology is poised to grow dramati-
cally among a range of industries and organizations.
Usage isnt limited to one company size, type or industry, as solid-state
is simply democratic, horizontally applicable fast storage, he said. 2
Alan Earls is a frequent contributor to various sites within the TechTarget Storage
Media Group.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
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wSTORAGE Essential Guide to Solid-State Storage Implementation Choices
ITH THE RISE of server virtualization and the general trend toward more
data, at one time or another most organizations need more storage per-
formance, particularly IOPS. At the device level, solid-state storage seems
to be the technology to provide it. But the devils in the details, which in
this case means implementation. Choosing how solid-state storage is put
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
28
CHANNEL SPIN:Implementing SSD ina cache appliance
Learn about the benefits of using solid-state storage
in a cache appliance, how the appliance compares
with other SSD implementations and why storageVARs should pay attention. By Eric Slack
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into a storage infrastructure can determine how effectively performance
is delivered to applications, which in the end is what really matters.Implementation of solid-state storage can take a number of different
physical forms, like drive form-factor solid-state drives (SSDs) that replace
hard disk drives in a server, or storage array or flash PCI Express (PCIe)
boards that install into a server. Another alternative can be a dedicated
flash storage array or appliance installed on the storage network.
Implementation can take different logical forms as well, like creating a
new tier 0 high-performance storage area in which to move performance-
critical application data during periods of highest activity. Or it can be a
cache appliance that holds a copy of this data thats still maintained on the
existing storage areas and updated when their cache session is terminated.
Well focus on the latter of these, the caching appliance implementation,
in which an independent storage device is installed in the environment and
shared by one or more servers or storage systemseither block or NAS.
Well detail the advantages of caching
appliances and discuss some impli-
cations for value-added resellers
(VARs) selling these solutions.
WHY A CACHE APPLIANCE MAKES SENSE
Simply replacing hard disk drives in aserver or existing storage array with
SSDs can be the easiest solution.
But it often means the SSDs cant be
used to their full capability because
existing hard drive controller archi-
tectures typically dont provide the
IOPS or connectivity SSDs require. In
addition, the lack of density and cost
per gigabyte of these implementations can force users to settle for less
(or more) capacity than needed, resulting in efficiency tradeoffs and low-
er performance. Dedicating SSDs to specific servers or storage systems
also reduces opportunities to share this high-priced resource, which
results in fewer applications receiving a performance boost, fewer
systems being included in the cost justification and increased manage-
ment overhead.
A caching appliance isnt a storage array but an independent high-speed
device thats purpose-built for solid-state drives and can be shared by mul-
tiple back-end storage systems. These standalone systems can address a
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
29
A caching applianceisnt a storage arraybut an independenthigh-speed devicethats purpose-builtfor solid-state drivesand can be shared bymultiple back-endstorage systems.
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STORAGE
STORAGE Essential Guide to Solid-State Storage Implementation Choices
number of issues the industry has had implementing solid-state storage
devices in its quest to improve application performance:
Shared performance and utilization benefits. IOPS requirements of stor-
age devices are constantly changing depending on the workloads of the
servers theyre supporting. While installing SSDs into a specific NAS or
block storage array can improve performance, it often results in periods of
low utilization when the servers using that individual storage system are
less active. An independent caching appliance, on the other hand, can be
shared across multiple storage systems, enabling higher asset utilization
and improved application performance for more servers. It can also provide
better ROI justification for an SSD upgrade project as the costs are spread
across more applications. This can make even more specialized devices,like DRAM, cost-effective, further improving performance of the appliance.
In some use cases, a caching appliance can turn one or more midrange
disk systems into a performance solution for less money than a compa-
rable high-end system.
Capacity benefits. A shared cache appliance can provide enough capacity
to pin an entire data set into solid-state storage. This can result in better
performance with fewer cache misses and better efficiency, as data move-
ment between solid-state and disk storage is greatly reduced. And the
effective capacity of the cache can be extended by combining multiple
storage types, like SSD and high-speed disk, into the same appliance.Lower processing overhead than tiered storage. Compared with a tier 0
implementation of solid-state storage, this appliance is a true cache,
which means it takes a copy of the most active or performance-critical
data sets. Tiered storage solutions that typically reside on the storage con-
troller move data into and out of the high-speed storage space, generating
processing overhead and reducing efficiency. These automated tiering
systems also require a warm-up period in which usage information about
new data sets is accumulated before they can move data, sometimes
taking hours or days.
No impact on data protection. Because the data set is maintained on theprimary storage system, data protection isnt affected by the caching appli-
ance. Storage serviceslike snapshots, replication and data deduplication
can be kept on the existing back-end storage systems and not added to the
cache CPU, helping to maintain performance.
Nondisruptive implementation. Finally, implementation of the caching
appliance is less disruptive because it involves only copying data sets,
not moving them from existing storage.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
30
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STORAGE Essential Guide to Solid-State Storage Implementation Choices
Sometimes referred to as a memory array as opposed to a storage
array, caching appliances are designed from the ground up to supportsolid-state storage. This means their architectures provide the IOPS re-
quired to feed many more solid-state devices than a traditional storage
array can. This in turn produces better storage density and higher capacity,
with the benefits mentioned above. It also eliminates the potential situa-
tion of legacy disk array shelves running nearly empty because they can
support only a handful of solid-state drives. Besides density, this results in
better efficiency as more flash cells can be made available in the memory
array for overhead processes like garbage collection.
BOTTOM LINE FOR VARsFor organizations that need better application performance, solid-state
storage technologies are certainly a viable option. But given the number
of SSD products available and because they arent a straight plug replace-
ment upgrade for spinning disk drives, many VARs customers may need
some help designing a solid-state solution. This should mean opportunity
for storage integrators.
Caching appliances can supply VARs with a strong solution candidate
when it comes to a solid-state storage performance upgrade. These systems
can be used to spread the performance of SSDs across multiple storage
systems, enabling better ROI than putting SSDs into individual storagearrays or servers. They can also provide the density and capacity to support
larger data sets, thereby improving efficiency and lowering overall costs.
From an implementation perspective, a caching appliance can be less dis-
ruptive than adding an SSD tier 0 to an existing storage infrastructure and
can complement the storage services and data protection already in place.
While not the only solid-state storage alternative available to storage VARs,
caching appliances should certainly be on the line card. 2
Eric Slack is a senior analyst at Storage Switzerland.
Solid-statestorage fore 21st century
Making aase for SSDs
Solid-statease studies
os and cons:MLC vs. SLC
MLC for theenterprise
SSD makesinroads
with SMBs
SD in a cacheappliance
31
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Essential Guide toSolid-State Storage Implementation Choices
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