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© 2009 EMC Corporation. All rights reserved.
Storage System EnvironmentStorage System Environment
Module 1.2
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 2
Storage System Environment
Upon completion of this module, you will be able to:
List components of storage system environment– Host, connectivity and storage
List physical and logical components of hosts
Describe key connectivity options
Describe the physical disk structure
Discuss factors affecting disk drive performance
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 3
Lesson: Components of Storage System Environment
Upon completion of this lesson, you will be able to:
Describe the three components of storage system environment– Host, Connectivity and Storage
Detail Host physical and logical components
Describe interface protocol– PCI, IDE/ATA and SCSI
Describe storage options– Tape, optical and disk drives
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 4
Host
Applications runs on hosts
Hosts can range from simple laptops to complex server clusters
Physical components of host– CPU
– Storage Disk device and internal memory
– I/O device Host to host communications
Network Interface Card (NIC)
Host to storage device communications
Host Bus Adapter (HBA)
LaptopServer
Mainframe
Group of Servers
LAN
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 5
Host: Logical Components
Host
DBMS
HBA HBA HBA
Applications
Volume Manager
Operating System
File System
Device Drivers
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 6
Logical Components of the Host
Application – Interface between user and the host
– Three-tiered architecture Application UI, computing logic and underlying databases
– Application data access can be classifies as: Block-level access: Data stored and retrieved in blocks, specifying the
LBA File-level access: Data stored and retrieved by specifying the name and
path of files
Operating system– Resides between the applications and the hardware
– Controls the environment
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 7
Logical Components of the Host (Cont)
Device Drivers– Enables operating system to recognize the device
– Provides API to access and control devices
– Hardware dependent and operating system specific
File System– File is a collection of related records or data stored as a unit
– File system is hierarchical structure of files Examples: FAT 32, NTFS, UNIX FS and EXT2/3
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 8
File System: Metadata Examples
UNIX (UFS)
File type and permissions
Number of links
Owner and group IDs
Number of bytes in the file
Last file access
Last file modification
Windows (NTFS)
Time stamp and link count
File name
Access rights
File data
Index information
Volume information
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 9
File Systems: Journaling and Logging
Improves data integrity and system restart time over non-journaling file systems.
Uses a separate area called a log or journal.– May hold all data to be written
– May hold only metadata
Disadvantage - slower than other file systems.– Each file system update requires at least 1 extra write – to the
log
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 10
Logical Components of the Host: LVM Responsible for creating and controlling
host level logical storage– Physical view of storage is converted to a
logical view by mapping– Logical data blocks are mapped to physical
data blocks
Usually offered as part of the operating system or as third party host software
LVM Components:– Physical Volumes– Volume Groups– Logical Volumes
Physical Storage
Logical Storage
LVM
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 11
Volume Groups One or more Physical Volumes
form a Volume Group
LVM manages Volume Groups as a single entity
Physical Volumes can be added and removed from a Volume Group as necessary
Physical Volumes are typically divided into contiguous equal-sized disk blocks
A host will always have at least one disk group for the Operating System– Application and Operating
System data maintained in separate volume groups
Logical Disk Block
Volume Group
Physical Disk Block
Physical Volume 1 Physical Volume 2 Physical Volume 3
Logical Volume
Logical Volume
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 12
LVM Example: Partitioning and Concatenation
Partitioning Concatenation
Logical Volume
Physical Volume
Servers
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 13
LVM Example
A Windows XP system with two physical hard disks.
Physical DiskPartition Filesystem Drive Letter
Hard Disk 1 Partition 1 NTFS C:Partition 2 FAT32 D:
Hard Disk 2 Partition 1 FAT32 E:
"C:", "D:", and "E:" are volumes. Hard Disk 1 and Hard Disk 2 are physical disks. Any of these can be called a "drive".
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 14
How Files are Moved to and from Storage
1 2 3
456
Consisting of Mapped by LVM to
Teacher (User)Course File(s) File System Files
File System Blocks
LVM Logical Extents
Disk Physical ExtentsDisk Sectors
Configures/Manages
Residing in
Reside in Mapped by a file system to
Managed by disk storage subsystem
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 15
Connectivity
Interconnection between hosts or between a host and any storage devices
Physical Components of Connectivity are:– Bus, port and cable
CPU HBA
Port
CableBUS
Disk
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 16
Bus Technology
Serial
Serial Bi-directional
Parallel
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 17
Bus Technology
System Bus – connects CPU to Memory
Local (I/O) Bus – carries data to/from peripheral devices.
Bus width measured in bits
Bus speed measured in MHz
Throughput measured in MB/S
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 18
Connectivity Protocol
Protocol = a defined format for communication between sending and receiving devices
– Tightly connected entities such as central processor to RAM, or storage buffers to controllers (example PCI)
– Directly attached entities connected at moderate distances such as host to storage (example IDE/ATA)
– Network connected entities such as networked hosts, NAS or SAN (example SCSI or FC)
Tightly ConnectedEntities
DirectlyAttachedEntities
Network Connected
Entities
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 19
Popular Connectivity Options: PCI
PCI is used for local bus system within a computer
It is an interconnection between microprocessor and attached devices
Has Plug and Play functionality
PCI is 32/64 bit
Throughput is 133 MB/sec
PCI Express – Enhanced version of PCI bus with higher throughput and clock
speed
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 20
PCI
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 21
Popular Connectivity Options: IDE/ATA
Integrated Device Electronics (IDE) / Advanced Technology Attachment (ATA)– Most popular interface used with modern hard disks
– Good performance at low cost
– Inexpensive storage interconnect
– Used for internal connectivity
Serial Advanced Technology Attachment (SATA)– Serial version of the IDE /ATA specification
– Hot-pluggable
– Enhanced version of bus provides upto 6Gb/s (revision 3.0)
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 22
PATA
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 23
SATA
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 24
Popular Connectivity Options: SCSI
Parallel SCSI (Small computer system interface)– Most popular hard disk interface for servers
– Higher cost than IDE/ATA
– Supports multiple simultaneous data access
– Used primarily in “higher end” environments
– SCSI Ultra provides data transfer speeds of 320 MB/s
Serial SCSI– Supports data transfer rate of 3 Gb/s (SAS 300)
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 25
SCSI-Bus Interface Connector
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 26
SCSI - Pros and Cons
Pros:– Fast transfer speeds, up to 320
megabytes per second
– Reliable, durable components
– Can connect many devices with a single bus, more than just HDs
– SCSI host cards can be put in almost any system
– Full backwards compatibility
Cons:– Configuration and setup
specific to one computer
– Unlike IDE, few BIOS support the standard
– Overwhelming number of variations in the standard, hardware, and connectors
– No common software interfaces and protocol
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 27
Comparison IDE/ATA vs SCSI
Feature IDE/ATA SCSI
Connectivity Market Internal Storage Internal and External Storage
Speed (MB/sec) 100/133/150 320
Hot Pluggable No Yes
Expandability Easier to set up Very good but veryexpensive to set up
Cost/Performance Good High cost/Fasttransfer speed
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 28
Storage: Medias and Options
Magnetic Tape– Low cost solution for long term data storage– Limitations
Sequential data access, Single application access at a time, Physical wear and tear and Storage/retrieval overheads
Optical Disks– Popularly used as distribution medium in small, single-user
computing environments– Write once and read many (WORM): CD-ROM, DVD-ROM– Limited in capacity and speed
Disk Drive– Most popular storage medium with large storage capacity– Random read/write access
Ideal for performance intensive online application
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 29
Lesson Summary
Key points covered in this lesson:
Host components– Physical and Logical
Connectivity options– PCI, IDE/ATA, SCSI
Storage options– Tape, optical and disk drive
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 30
Lesson: Disk Drive
Upon completion of this lesson, you will be able to:
List and discuss various disk drive components– Platter, spindle, read/write head and actuator arm assembly
Discuss disk drive geometry
Describe CHS and LBA addressing scheme
Disk drive performance– Seek time, rotational latency and transfer rate
Law’s governing disk drive performance
Enterprise flash drive
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 31
Disk Drive Components
Interface
Controller
Power Connector
HDA
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 32
Physical Disk Structure
Sector
Track
Platter
SectorTrack
Cylinder
Spindle
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 33
Logical Block Addressing
Physical Address= CHS
Cylinder 2
Head 0
Sector 10
Block 48
Block 16
Block 32
Logical Block Address= Block#
Block 0
Block 8
(Upper Surface)
(Lower Surface)
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 34
Platter Geometry and Zoned-Bit Recording
Platter Without Zones
Sector
Track
Platter With Zones
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 35
Disk Drive Performance
Electromechanical device– Impacts the overall performance of the storage system
Disk Service Time– Time taken by a disk to complete an I/O request
Seek Time Rotational Latency Data Transfer Rate
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 36
Disk Drive Performance: Seek Time
Time taken to position the read/write head
Lower the seek time, the faster the I/O operation
Seek time specifications include:– Full stroke
– Average
– Track-to-track
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 37
Disk Drive Performance: Rotational Speed/Latency
The time taken by platter to rotate and position the data under the R/W head
Depends on the rotation speed of the spindle
Average rotational latency – One-half of the time taken for a full
rotation
– Appx. 5.5 ms for 5400-rpm drive
– Appx. 2.0 ms for 15000-rpm drive
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 38
Disk Drive Performance: Data Transfer Rate
Average amount of data per unit time
Internal Transfer Rate– Speed at which data moves from a track to disk internal buffer
External Transfer Rate– The advertised speed of the interface
InterfaceInterface BufferBufferHBAHBA
Disk Drive
Internal transfer rate measured here
External transfer rate measured here
Head Disk AssemblyHead Disk Assembly
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 39
SATA vs SAS drives in 3.5-in form factor in 2006
Power consumed by the disk motor:Power Diameter4.6 ×RPM2.8 × Number of platters
Power Consumption
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 40
Fundamental Laws Governing Disk Performance
Little’s Law– Describes the relationship between the number of requests in a queue and the
response time.
– N = a × R “N” is the total number of requests in the system “a” is the arrival rate “R” is the average response time
Utilization law– Defines the I/O controller utilization
– U = a × RS
“U” is the I/O controller utilization “RS“ is the service time
126 5 4 3I/O
ControllerProcessed I/O Request
ArrivalI/O Queue
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 41
Utilization vs. Response time
Consider a disk I/O system in which an I/O request arrives at a rate of 100 I/Os per second. The service time, RS, is 4 ms. – Utilization of I/O controller (U = a × Rs) – Total response time (R=Rs /1–U) – Time spent by a request in a queue Rq = Rs U /(1–U) – Average queue size = U2 / (1–U)
Calculate the same with service time is doubled
0% 100%Utilization
Knee of curve: disks at
about 70% utilization
Low Queue Size
70%
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 42
Application Requirements and Disk Performance
Exercise:
Consider an application that requires 1TB of storage capacity and performs 4900 IOPS – Application I/O size is 4KB– As it is business critical application, response time must be
within acceptable range
Specification of available disk drive:– Drive capacity = 73 GB – 15000 RPM– 5 ms average seek time– 40 MB/sec transfer rate
Calculate the number of disks required?
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 43
Solution
Calculate time required to perform one I/O Seek time + (rotational delay)/speed in RPM + (block size/transfer rate)
Therefore, 5 ms + 0.5 /15000 + 4K/40MB = 7.1 msec
Calculate max. number of IOPS a disk can perform– 1 / 7.1 ms = 140 IOPS
For acceptable response time disk controller utilization must be less than 70%– Therefore, 140 X 0.7 = 98 IOPS
To meet application – Performance requirement we need 4900/98 i.e. 50 disk– Capacity requirement we need 1TB/ 73 GB i.e. 14 disk
Disk required = max (capacity, performance)
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 44
Enterprise Flash Drives: A New Generation Drives
Conventional disk drive
Mechanical Delay associated with conventional drive
– Seek time
– Rotational latency
More power consumption due to mechanical operations
Low Mean Time Between Failure
Enterprise flash drive
Highest possible throughput per drive– No Spinning magnetic media– No Mechanical movement which
causes seek and latency– Solid State enables consistent I/O
performance
Very low latency per I/O
Energy efficient storage design– Lower power requirement per GB of
storage
– Lower power requirement per IOPS
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 45
Enterprise Flash Drives – Overview
Drive is based on Flash Solid State memory technology– High performance and low latency
– Non volatile memory
– Uses single layer cell (SLC) or Multi Level cell (MLC) to store data
Enterprise Flash Drives use a 4Gb FC interface
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 46
Enterprise Flash Drives – Benefits
Faster performance– Up to 30 times greater IOPS
(benchmarked)
– Typical applications: 8 – 12X
– Less than 1 millisecond service time
More energy efficient– 38 percent less per terabyte
– 98 percent less per IO
Better reliability– No moving parts
– Faster RAID rebuilds
IO per secondR
esp
on
se T
ime
1 Flash drive
1@15K FibreChannel drive
10@15K Fibre Channeldrives
30@15KFibre
Channel drives
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 47
Enterprise Flash Drives – “Tier-0” Application
Position Enterprise Flash Drives as the high-performance option in demanding environments– Low latency applications, also known as “Tier-0”
applications
Standard form-factor and capacity design allows for easier integration
High performance, low power for a “Green” initiative
Target Customer/Market Segments:– High performance solutions coupled with low power– Specifically target Oracle database customers initially– Financial trading– OLTP databases
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 48
Lesson Summary
Key points covered in this lesson:
Disk drive components and geometry
Disk drive addressing scheme
Disk drive performance
Convention drive Vs Enterprise Flash Drives
Enterprise Flash Drives for high performance and low power storage solution
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 49
Module Summary
Key points covered in this module:
Storage system environment components:– Host, connectivity and storage
Physical disk structure and addressing
Factors affecting disk performance
Flash drives benefits
© 2009 EMC Corporation. All rights reserved. Storage System Environment - 50
Check Your Knowledge
What are some examples of hosts?
What are the physical and logical components of a host?
What are the common connectivity protocols used in computing environments?
What is the difference between seek time and rotational latency?
What is the difference between internal and external data transfer rates?