Disk Storage Systems
Module 2.5
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Disk Storage Systems
After completing this module, you will be able to:
 Describe the components of an intelligent storage system
 Describe the configuration of a logical disk
 Discuss the methods employed to ensure that a host can
access a storage volume
 Discuss back end volume protection
 Discuss front end host configuration
 Describe the I/O flow from the back end to the physical
disks
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Disk Storage Systems - 2
Lesson: Intelligent Storage System Overview
After completing this lesson, you will be able to:
 List the benefits of intelligent storage systems
 Compare and contrast integrated and modular
approaches to intelligent storage systems
 Describe the I/O flow through the storage system
 Describe the logical elements of an intelligent storage
system
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What is an Intelligent Storage System?
 A disk storage system which distributes data over several
devices and manages access to that data.
 When implemented properly, it provides the following
benefits over individual storage devices:
– Increased capacity
– Improved performance
– Easier data management
– Better data availability
– More robust backup/restore capabilities
– Improved flexibility and scalability
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Disk Storage Systems - 4
Monolithic (Integrated) Storage Systems
FC Ports
Port Processors
Monolithic
Cache
RAID Controllers
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Modular Storage Systems
Modular
Rack
Host Interface
Host Interface
Servers
Cache
Cache
RAID
RAID
Controller A
Controller B
FC Switches
Disk Modules
Control Module
with Disks
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Elements in an Intelligent Storage System
Intelligent Storage System
Front End
Host
Connectivity
Back End
Physical Disks
Cache
Cache
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Intelligent Storage System: Front End
Intelligent Storage System
Front End
Host
Physical Disks
Cache
Connectivity
Ports
Back End
Controllers
Note: Include redundancy in the channels to and from the ports.
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Disk Storage Systems - 8
Front End Command Queuing
Without Command Queuing
Request 1
Request 2
Request 3
Request 4
F
R
O
N
T
E
N
D
4
3
2
2
1
1
3
4
With Command Queuing
Request 1
Request 2
Request 3
Request 4
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F
R
O
N
T
E
N
D
4
2
3
2
1
1
3
4
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Intelligent Storage System: Cache
Intelligent Storage System
Front End
Host
Connectivity
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Back End
Physical Disks
Cache
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Intelligent Storage System: Back End
Intelligent Storage System
Front End
Host
Connectivity
Back End
Cache
Controllers
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Physical Disks
Ports
Disk Storage Systems - 11
Intelligent Storage System: Physical Disks
Intelligent Storage System
Front End
Host
Connectivity
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Back End
Physical Disks
Cache
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I/O Example: Read Requests
Intelligent Storage System
Front End
Host
Connectivity
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Back End
Physical Disks
Cache
Disk Storage Systems - 13
I/O Example: Write Requests
Intelligent Storage System
Front End
Host
Connectivity
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Back End
Physical Disks
Cache
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What the Host Sees
Intelligent Storage System
Host
Back End
LUN 0
LUN 1
Physical Disks
Cache
Host
LUN 2
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LUN 0
LUN 1
LUN 2
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The Host and Logical Device Names
Intelligent Storage System
Host
Volume
Manager
/dev/rdsk/c1t1d0
/dev/rdsk/c1t1d1
Back End
LUN 0
LUN 1
Physical Disks
Cache
Host
Volume
Manager
LUN 2
LUN 0
LUN 1
LUN 2
\\.\PhysicalDrive0
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Disk Storage Systems - 16
Disk Organization in a Storage System
Intelligent Storage System
Host
Back End
LUN 0
Cache
Physical Disks
LUN 0
LUN 1
Host
LUN 1
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Disk Storage Systems - 17
Lesson Summary
Key points covered in this lesson:
 An intelligent disk storage system:
– Distributes data over several devices and manages access to that
data
– Has a front end, cache, a back end, and physical disks.
– Use the virtual disks to provide optimal performance and capacity.
– Individual disks within a RAID set can be divided into logical units.
– The same concept can be applied to entire RAID sets.
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Disk Storage Systems - 18
Lesson: Cache – A Closer Look
After completing this lesson, you will be able to:

Define cache

Distinguish between multipurpose cache and
configurable cache

Describe cache hits and misses

Describe algorithms to manage cache

Trace the I/O flow from the cache to the back end to the
physical disks
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Disk Storage Systems - 19
What is Cache in a Storage System
A memory space used by a disk storage system to
reduce the time required to read data/write data. It is
usually made from very fast memory
Cache
Read
Write
Request
Acknowledgment
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Disk Storage Systems - 20
How Cache is Structured
Data Store
Tag RAM
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Read Cache ‘Hits’ and ‘Misses’
Data found in cache = ‘Hit’
Cache
Read
Request
No data found = ‘Miss’
Cache
Read
Request
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Disk Storage Systems - 22
Algorithms Used to Manage Read Cache
New Data
 Least Recently Used (LRU)
– Determines which items are
accessed frequently/infrequently
– Discards least recently used data
Oldest Data
 Read Ahead (pre-fetch)
– Accesses data sequentially and puts
it into cache before it is requested
– May assume that data recently
accessed will not be needed again.
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Disk Storage Systems - 23
Write Algorithms
Write-through Cache
Cache
Write
Request
Acknowledgement
Write-back
Cache
Write
Request
Acknowledgement
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Write Cache: Performance
 Manage peak I/O requests “bursts” through flushing
– Least-recently used pages are flushed from cache to the drives
 For maximum performance:
– Provide headroom in write cache for I/O bursts
 Coalesce small host writes into larger disk writes
– Improve sequentiality at the disk
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Lesson Summary
Key points covered in this lesson:
 Cache is a memory space used by a disk storage system
to reduce the time required to read data/write data.
 It can speed up both read and write operations.
 Cache read algorithms include:
– Least Recently Used (LRU)
– Read Ahead (pre-fetch)
 Cache write algorithms include:
– Write-through
– Write-back
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Disk Storage Systems - 26
Module Summary
Key points covered in this module:
 An intelligent disk storage system distributes data over
several devices and manages access to that data.
 Monolithic storage systems are generally aimed at the
enterprise level, centralizing data in a powerful system
with hundreds of drives.
 Modular storage systems provide storage to a smaller
number of (typically) Windows or Unix servers than larger
integrated storage systems.
 Cache is an important part of intelligent disk storage
systems as it can be used to improve performance.
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Disk Storage Systems - 27
 Check Your Knowledge
 What are the parts of an Intelligent Disk Subsystem?
 What is the difference between a monolithic and a
modular array?
 What is the difference between cache hit and a cache
miss?
 What is the difference between Least Recently Used and
Read Ahead cache?
 What is the difference between Write-through and Writeback cache?
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Disk Storage Systems - 28
Apply Your Knowledge
Upon completion of this case study, you will be able to:
 Describe the basic architecture of the CLARiiON modular
storage array.
 Describe the basic architecture of the Symmetrix
integrated storage array.
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Disk Storage Systems - 29
CLARiiON CX3-80 Architecture
UltraScale
Storage Processor
1/2/4 Gb/s Fibre Channel Front End
UltraScale
Storage Processor
CLARiiON Messaging Interface (CMI)
Multi-Lane PCI-Express bridge link
Fibre Channel
CPU
Fan
CPU
FC FC FC
FC
2/4 Gb/s Fibre
Channel Back End
SPS
Power supply
Mirrored cache
SPS
Fan
Fan
Fibre Channel
Fan
Mirrored cache
CPU
CPU
FC FC FC FC
Power supply
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
4Gb/s LCC
2/4 Gb/s Fibre
Channel Back End
Up to 480 drives max per storage system (CX3-80)
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Disk Storage Systems - 30
Assigning CLARiiON LUNs to Hosts
 CLARiiON disks are grouped into RAID Groups
– Disks from any enclosure may be used in a RAID Group
– All disks in a RAID Group must be either Fibre Channel or ATA
– A RAID Group is the ‘RAID set’ discussed earlier
– A RAID Group may be a single disk, or RAID Level 0, 1, 1/0, 3 or 5
 The RAID Group is then partitioned into LUNs
– All LUNs in a RAID Group will be the same RAID Level
 The LUNs are then made accessible to hosts
– CLARiiON-resident software ensures that LUNs are seen only by the
hosts that own them
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Disk Storage Systems - 31
EMC Symmetrix DMX Array
 Direct Matrix Interconnect
 Dynamic Global Memory
 Enginuity Operating Environment
 Processing Power
 Flexible Back-End Configurations
 Fault-tolerant Design
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Disk Storage Systems - 32
Symmetrix DMX Series Direct Matrix Architecture
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Disk Storage Systems - 33
Symmetrix DMX: Dual-ported Disk and Redundant Directors
Disk Director 16
Disk Director 1
S
P
S
P
S
P
S
P
P
S
P
S
P
S
P
S
P = Primary Connection to Drive
S= Secondary Connection for Redundancy
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Disk Storage Systems - 34
Configuring Symmetrix Logical Volumes (SLV)
Physical
Disk
Physical
Disk
Physical
Disk
Physical
Disk
Physical
Disk
Symmetrix Service Processor
Running SymmWin Application
 Initial configuration of Symmetrix Logical Volumes is done
via the Symmetrix Service Processor and the SymmWin
interface/application
– A configuration file (IMPL.BIN) is created and loaded on to the array
 Subsequent configuration changes can be performed
online using EMC ControlCenter (GUI) or by using
Solutions Enabler (CLI)
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RAID1 – Symmetrix Logical Volume
 RAID1 SLV
– Data is written to two hyper volumes on two different physical disks
which are accessed via two different disk directors
 Host is unaware of data protection being applied
Different Disk
Director
Disk Director
Physical
Drive
Hyper
Logical Volume
04B
Physical
Drive
LV 04B M2
Host Address
Target = 1
LUN = 0
Volumes
LV 04B M1
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Disk Storage Systems - 36
Data Protection
 Mirroring (RAID 1)
– Highest performance, availability and functionality
– Two hyper mirrors form one Symmetrix Logical Volume located on separate
physical drives
 Parity RAID (Not available on DMX3)
– 3 +1 (3 data and 1 parity volume) or 7 +1 (7 data and 1 parity volume)
 Raid 5 Striped RAID volumes
– Data blocks are striped horizontally across the members of the RAID group
( 4 or 8 member group); parity blocks rotate among the group members
 RAID 10 Mirrored Striped Mainframe Volumes
 Dynamic Sparing
 SRDF (Symmetrix Remote Data Facility)
– Mirror of Symmetrix logical Volume maintained in a separate Symmetrix
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Disk Storage Systems - 37
Assigning Symmetrix Logical Volumes to Hosts
 Configure Symmetrix Logical Volumes
 Map Symmetrix Logical Volumes to Front-end ports
– Performed via EMC ControlCenter or Solutions Enabler
 Make Symmetrix Logical Volumes accessible to hosts
– SAN Environment
 Zone Hosts to Front-end ports
 Perform LUN Masking
 Can be performed via EMC ControlCenter or Solutions Enabler
 LUN Masking information is maintained on the Symmetrix in the VCM Database
(VCMDB)
■ LUN Masking information is also flashed to all the front-end directors
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