Storage School I

An introduction to the world of storage

Storage School I: An introduction to the world of storage

Presented by Stephen FoskettDirector of the Data Practice

Contouralsfoskett@contoural.com

www.contoural.com

The world of storage can be daunting the uninitiated. This session provides all of the

background that you will need to get started in the world of storage. We will start with the basic

concepts: SAN vs. NAS, block vs. file, RAID levels, and other basic topics. These are woven together in a lively lesson, explaining how we got here and why it all matters. We will finish up with a brief

discussion of how storage fits within the big picture of enterprise IT.

WHAT I ASSUME YOU KNOW

• Storage School I assumes no prior knowledge of storage topics, but a basic comprehension of computing and networks would be helpful.

BY THE END OF THE SESSION, YOU’LL KNOW THE FOLLOWING:

• A bit of history and context• Five Important Concepts:

• Storage outside the computer• Blocks and files• The importance of SCSI• What RAID is and why it’s important• The three kinds of storage arrays

• How it all fits together in a storage architecture

How involved with storage are you?1. I’m soaking in it! (it’s my job)2. Touch and go (I’m involved but not all the time)3. I just stepped in quicksand! (I’m new to all this)4. Cardboard boxes and tape! (what’s this all about?)

NIL NOVI SUB SOLE(There Is Nothing New Under The Sun)

• The basic concepts of storage are not new and most are easy to grasp once the reasoning and history behind them is understood

• Simply put, the storage world of today is the result of consolidation, networking, and sharing of resources

• We mostly talk about open systems now, but much of the work was pioneered in the world of mainframes and minicomputers

Important Concept #1:Storage is Outside the Computer

• Mainframe storage has always been located in a separate cabinet• IBM introduced the first disk drive system in 1956,

the 350 disk storage unit• The storage industry was born with “plug-

compatible” storage for the System/360’s 2311 and 2314 DAS in the 1960s

• Bus-and-tag became ESCON in 1990• Open systems storage moved outside later

• Seagate’s 1980 introduction of the ST506 brought hard disk storage to the personal computer

• Introduced in 1986, SCSI allowed personal computers and servers to access external storage

IBM 350

IBM 2314

ST506

ESCON

SCSI

We’re Used to External Storage Today

• External disks are common from PCs to servers• FireWire and USB storage is used on PCs• External Serial ATA (eSATA) is becoming more

common• Servers still use SCSI, but also commonly use Fibre

Channel• Networked storage is also gaining attention

• NAS and iSCSI use common Ethernet and IP protocols

• Enterprise storage generally consists of SCSI, Fibre Channel, and Ethernet

FireWire and USB

eSATA

Ethernet

Fibre Channel

Important Concept #2:Blocks and Files

• Disk drives (and things like disk drives) organize data in blocks• Equal-sized units have unique addresses on the disk

• People (and most applications) organize data as files in folder hierarchies

• Filesystem drivers in the operating system translate file requests to block addresses

Most Enterprise Storage Systems and Protocols are Block or File Based

• Block protocols require a filesystem driver in the computer to locate files• SCSI, Fibre Channel, and iSCSI• Also USB, FireWire, thumb drives – anything that acts like a

disk drive• File-based devices handle the file translation and

organization themselves• File servers and NAS arrays return data based on directory

location and filename• Content-addressable storage (CAS) is something

else altogether• CAS uses a hash of the content itself (block or file) to

create a unique address for data

SAN and NAS

• A storage area network (SAN) is a block storage network• SCSI “initiators” (servers) talk to “targets” (disks or arrays)

and request access to logical sets of block storage (LUNs)• SAN implies FC or iSCSI storage

• Network-attached storage (NAS) is a file storage network• Clients request files from file servers or NAS arrays

(“filers”)• Common NAS protocols include CIFS/SMB for Windows and

NFS for UNIX• A network of NAS devices has been dubbed a file area

network (FAN)

Important Concept #3:Most Enterprise Block Storage Uses SCSI

• SCSI is the foundation of all current enterprise block storage protocols• “SCSI” is both a command set and physical

specification• Thick parallel SCSI cables of old have been

replaced by new connections• “Fibre Channel” = SCSI commands over Fibre

Channel Protocol on optical fiber or copper cables• iSCSI = SCSI commands over TCP/IP, commonly

over Ethernet• SAS = SCSI commands over some FCP services and

a serial transport based on Serial ATA (SATA)• Mainframes now use FICON which is like

ESCON over FCP (not SCSI)

SCSI commands

FCP

Optical/Copper

“Fibre Channel”

SCSI commands

Partial FCP

SATA Copper

Serial Attached SCSI (SAS)

SCSI commands

TCP/IP

Optical/Copper

iSCSI

Ethernet/other

…But other protocols are used by disk drives

• Serial ATA (SATA) is used in lower-end drives • Replaced parallel ATA, also called IDE• SATA is quick, common, and cheap

• Serial-Attached SCSI (SAS) is the next tier• Replaced parallel SCSI as higher-end drive• Shares common components with SATA but adds SCSI

command set (and “command queueing”)• Native Fibre Channel drives are still tops

• Have non-optical FC interconnect• Enterprise drives versus desktop drives

• Enterprise are more sturdy and pass more rigorous tests• Spinning speed (RPM) has huge impact on performance

Important Concept #4:RAID Combines Disks

• A Redundant Array of Independent Disks (RAID) is a combination of disk drives acting as one• RAID can improve performance and reliability

• RAID is as old as storage• IBM patented the general concept in 1978 • David Patterson, Garth Gibson, and Randy Katz defined

five idealized RAID “levels” in 1988• The “I” originally stood for “inexpensive”, but this proved

to be inaccurate once arrays were produced for sale!• Today there are literally dozens of different

implementations of the RAID concept

Common RAID Levels

RAID 0 “Stripe”• Poor reliability – no data

protection and double the chance of failure!

• No “wasted” space• Fast reads and writes – 2x!

RAID 1 “Mirror”• Good reliability• 50% overhead for data

protection• 50% “wasted” space• 2x fast reads but slower

writes

Common RAID Levels

RAID 4 “Dedicated parity”• Good data protection• Less “wasted” space (N-1)• Nx faster reads but slower

writes• Parity across blocks means

lots of recalculation if they’re not written at the same time

RAID 5 “Striped parity”• Good data protection• Less “wasted” space (N-1)• Nx faster reads but slower

writes• Parity for each block means

they can easily be written individually

PPPP

PP

PP

RAID Mashups

• It is common to “stack” RAID levels as “RAID X+Y” where “X” is laid over top of “Y”• RAID 0+1 (or RAID 01) is mirrored stripes• RAID 1+0 (or RAID 10) is striped mirrors• RAID 5+0 (or RAID 50) is striped RAID 5

• RAID 6 or RAID DP has two parity slots – either a duplicate or an alternate calculation

• RAID E mixes a hot spare disk into the striping• Some vendors use RAID on a region of a disk

instead of a whole disk drive

Grid array

Important Concept #5:There are Three Kinds of Storage Array

• Monolithic arrays are large cabinets with many disk slots, controllers, and I/O paths• IBM, EMC, and HDS started with the mainframe

• Modular arrays use a 1- or 2-controller “head” and generic disk shelves that can be added as needed• 3Com was followed by NetApp, CLARiiON, etc…• Clustered heads and SAN storage can be used

• Grid arrays have small nodes with a few drives that team up in flexible clusters for performance and reliability• Upstart CAS and iSCSI arrays were first to use this

concept

Monolithic array

Modular array

Choices Abound for Networked Enterprise

Storage• No matter if you’re looking for SAN, NAS, iSCSI, or

CAS there are lots of options• There are monolithic, modular, and grid devices that

support most protocols• Every type of equipment and protocol could

support every type of application• Databases can run great on NAS or RAID 5• You can build a cheap SAN with Fibre Channel or iSCSI• NAS filers can make great archiving targets• Workstations can share SAN storage• CAS can be accessed with NFS or CIFS• You can put tier-3 bulk storage on an enterprise array• Modular arrays can outrun their big brothers

Mixing Up the Right SAN

• The best choice is the one that makes the most sense in your environment

• Select the right tool for the job instead of using a wrench as a hammer• Just because something can work doesn’t make it a good

idea• Always pick the simplest and most straightforward solution

• Look for the best fit for your budget and scale• If you only have a few terabytes, buy just one networked

array that will work for most of your applications• Match your chosen technologies with the platforms

and applications you have

Architecture Example:Small Web Company

• A small but growing business focused on a web-based product• Wants stability, flexibility, scalability, low cost, and DR• All Windows, mostly file but with some block storage

• Selected a modular NAS/iSCSI array• NAS replaced all current Windows file servers• iSCSI replaced internal storage for email and database• Picked a midrange device with lots of growth potential• Used SATA drives with RAID 6 for reliability and “good

enough” performance• Built-in snapshots and replication of both file and block

data from a single interface

Architecture Example:Large Financial Company

• A household name in the world of finance• Wanted to implement tiered storage to save money• Hundreds of TB, mixed Windows, UNIX, and mainframe

• Selected a modular FC SAN device• Sufficient staff and money to bring in a new storage

platform• Spent time and money on data classification to move less

critical apps off Tier 1• Decided to consolidate Windows systems with

virtualization and blades rather than use iSCSI• Deferred all enterprise storage purchases for two years• Kept all mainframe data on Tier 1 enterprise storage for

now

Closing Thoughts

• Bring in the storage that is right for you• Don’t let “rules of thumb” and bogus “best practices”

prejudice your choice• All storage devices work pretty well these days -

but none are perfect• Don’t try to do anything exotic with basic devices• Use the right tool for the job

• Make the vendors prove it works• Talk to references who are doing what you want to do• Create a proof of concept before buying

• Remember that it’s not all about the technology – even the best storage can’t fill an uncertain need!

Questions?

• Audience Q&A: 10-15 minutes

• Contact me at sfoskett@contoural.com

• Come talk to me after the session or at lunch

• I'll be available at the Ask-the-Expert booth today and tomorrow from 5 PM to 6 PM

For More Information

• Contact me:• Stephen Foskett – sfoskett@contoural.com

• Visit SearchStorage.com and read Storage magazine

• Get SNIA’s "Network Storage Terms and Acronyms" book

• Ask others here at the show or at user groups• Storage Networking User Group (SNUG)

• http://storagenetworking.org• Association of Storage Networking Professionals (ASNP)

• http://asnp.org• Ask the vendors (really!)