Disk Storage Systems

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


Module 2.5

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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2

Intelligent 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

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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3

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

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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4

What is an Intelligent Storage System

Intelligent Storage Systems are RAID arrays that are:


Highly optimized for I/O processing.


Have large amounts of cache for improving I/O
performance.


Have operating environments that provide:

–
Intelligence for managing cache

–
Array resource allocation

–
Host access to array resources

–
Connectivity for heterogeneous hosts

–
Advanced array based local and remote replication options


© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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5

Benefits of an Intelligent Storage System

Intelligent storage system provides several benefits over a
collection of disks in an array or even a RAID array:

–
Improved performance

–
Easier data management

–
Improved resource allocation and utilization

–
Very high levels of data availability and data protection

–
Array based technologies for local and remote replication

–
Optimized backup/restore functionalities

–
Improved flexibility and scalability


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Disk Storage Systems


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Monolithic (Integrated) Storage Systems

Monolithic

FC Ports

Port Processors

Cache

RAID Controllers

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Disk Storage Systems


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Modular Storage Systems

Rack

Servers

Disk Modules

Control Module

with Disks

FC Switches

Modular

Host Interface

Cache

RAID

Controller A

Host Interface

Cache

RAID

Controller B

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Disk Storage Systems


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Components of an Intelligent Storage System

Intelligent Storage System

Cache

Front End

Back End

Cache

Physical Disks

Host

Connectivity

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Disk Storage Systems


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Intelligent Storage System: Front End

Intelligent Storage System

Ports

Host

Connectivity

Controllers

Front End

Back End

Cache

Physical Disks

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Disk Storage Systems


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Front End Command Queuing

F

R

O

N

T

E

N

D

Request 1

Request 2

Request 3

Request 4

1

2

3

4

F

R

O

N

T

E

N

D

Request 1

Request 2

Request 3

Request 4

1

3

2

4

Without Command Queuing

With Command Queuing

1

2

3

4

1

2

3

4

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Disk Storage Systems


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Intelligent Storage System: Cache

Intelligent Storage System

Host

Connectivity

Front End

Back End

Cache

Physical Disks

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Disk Storage Systems


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Intelligent Storage System: Back End

Host

Connectivity

Ports

Controllers

Front End

Back End

Cache

Physical Disks

Intelligent Storage System

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Disk Storage Systems


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13

Intelligent Storage System: Physical Disks

Host

Connectivity

Front End

Back End

Cache

Physical Disks

Intelligent Storage System

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Disk Storage Systems


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14

What the Host Sees
–

Physical Drive Partitioning

Intelligent Storage System

LUN 0

LUN 1

LUN 2

LUN 0

LUN 1

LUN 2

Host

Host

Back End

Physical Disks

Cache

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Disk Storage Systems


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15

What the Host Sees
–

RAID Sets and LUNs

Intelligent Storage System

LUN 0

LUN 1

Host

Host

LUN 0

LUN 1

Back End

Physical Disks

Cache

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Disk Storage Systems


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16

Logical Device Names

Host

Volume

Manager

Host

/dev/rdsk/c1t1d0

/dev/rdsk/c1t1d1

\
\
.
\
PhysicalDrive0

Volume

Manager

Intelligent Storage System

LUN 0

LUN 1

LUN 2

LUN 0

LUN 1

LUN 2

Back End

Physical Disks

Cache

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Disk Storage Systems


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17

Lesson Summary

Key points covered in this lesson:


An intelligent disk storage system:

–
Is highly optimized for I/O processing

–
Has an operating environment which, among other things, manages
cache, controls resource allocation, and provides advanced local and
remote replication capabilities

–
Has a front end, cache, a back end, and physical disks

–
The physical disks can be partitioned into LUNs or can be grouped
into RAID sets, and presented to the hosts

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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18

Lesson: Cache
–

A Closer Look

After completing this lesson, you will be able to:


Describe the benefit of cache in intelligent storage
systems


Describe how cache is structured


Describe cache hits and misses


Describe algorithms to manage cache

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Disk Storage Systems


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19

What is Cache in a Storage System

A memory space used by an intelligent storage system
to reduce the time required to service I/O requests from
the host

Cache

Read

Request

Write

Request

Acknowledgment

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Disk Storage Systems


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20

How Cache is Structured

Data Store

Tag RAM

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Disk Storage Systems


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Disk Storage Systems


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22

Read

Request

Read Cache ‘Hits’ and ‘Misses’

Cache

Read

Request

Cache

Data found in cache = ‘Hit’

No data found = ‘Miss’

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Disk Storage Systems


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23

Algorithms Used to Manage Cache


Least Recently Used (LRU)

–
Discards least recently used data


Most Recently Used (MRU)

–
Discards most recently used data


Read Ahead (pre
-
fetch)

–
Monitors read requests from hosts to
detect sequential access

–
If sequential access is detected, then
data is read from the disk into cache
before

it is requested by the host

New Data

Oldest Data

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Disk Storage Systems


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Write

Request

Write Algorithms

Write

Request

Write
-
through Cache

Write
-
back

Acknowledgement

Acknowledgement

Cache

Cache

Acknowledge
-

ment

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Disk Storage Systems


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25

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

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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26

Lesson Summary

Key points covered in this lesson:


Cache is a memory space used by an intelligent storage
system to reduce the time required to service I/O
requests from the host


Cache can speed up both read and write operations


Algorithms to manage cache include:

–
Least Recently Used (LRU)

–
Most Recently Used (MRU)

–
Read Ahead (pre
-
fetch)


Cache write algorithms include:

–
Write
-
through

–
Write
-
back

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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27

Module Summary

Key points covered in this module:


Intelligent Storage Systems are RAID Arrays that are
highly optimized for I/O processing


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 in intelligent storage systems accelerates
response times for host I/O requests

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Disk Storage Systems


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Check Your Knowledge


What are the parts of an Intelligent Storage System?


What are the differences between a monolithic and a
modular array?


What is the difference between a read cache hit and a
read cache miss?


What is the difference between Least Recently Used and
Most Recently Used algorithms?


What is the difference between Write
-
through and Write
-
back cache?



© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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29

Apply Your Knowledge

Upon completion of this case study, you will be able to:


Describe the basic architecture of the EMC CLARiiON
modular storage array


Describe the basic architecture of the EMC Symmetrix
integrated storage array

© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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CLARiiON CX3
-
80 Architecture

Power supply

Power supply

Fan

Fan

Fan

SPS

Up to 480 drives max per storage system (CX3
-
80)

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

4Gb/s LCC

UltraScale

Storage Processor

UltraScale

Storage Processor

Fibre Channel

Mirrored cache

Fibre Channel

CPU

Mirrored cache

CPU

FC

FC

CPU

FC

CPU

FC

FC

FC

FC

FC

Fan

2/4 Gb/s Fibre
Channel Back End

2/4 Gb/s Fibre
Channel Back End

1/2/4 Gb/s Fibre Channel Front End

CLARiiON Messaging Interface (CMI)

Multi
-
Lane PCI
-
Express bridge link

SPS

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Disk Storage Systems


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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


© 2007 EMC Corporation. All rights reserved.

Disk Storage Systems


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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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Symmetrix DMX Series Direct Matrix Architecture

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Disk Storage Systems


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Symmetrix DMX: Dual
-
ported Disk and Redundant Directors

Disk Director 1

Disk Director 16

P

S

P

S

P

S

P

S

S

P

S

P

S

P

S

P

P =
Primary Connection to Drive

S=
Secondary Connection for Redundancy

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Disk Storage Systems


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Configuring Symmetrix Logical Volumes (SLV)


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)

Physical
Disk

Physical
Disk

Physical
Disk

Physical
Disk

Physical
Disk

Symmetrix Service Processor

Running SymmWin Application

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Disk Storage Systems


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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

Physical
Drive

LV 04B M2

Different Disk
Director

Physical
Drive

LV 04B M1

Disk Director

Logical Volume
04B

Host Address

Target = 1

LUN = 0

Hyper

Volumes

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Disk Storage Systems


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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


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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