Disk Storage Systems

© 2007 EMC Corporation. All rights reserved.

Disk Storage SystemsDisk Storage Systems

Module 2.5

© 2007 EMC Corporation. All rights reserved. Disk Storage Systems - 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


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


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


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


Monolithic (Integrated) Storage Systems

Monolithic

FC Ports

Port Processors

Cache

RAID Controllers


Modular Storage Systems

Rack

Servers

Disk Modules

Control Modulewith Disks

FC Switches

Modular

Host Interface

Cache

RAID

Controller AController A

Host Interface

Cache

RAID

Controller BController B


Components of an Intelligent Storage System

Intelligent Storage System

CacheCache

Front End Back End

Cache

Physical Disks

Host Connectivity


Intelligent Storage System: Front End


Ports

Host Connectivity

Controllers

Front End Back End

Cache

Physical Disks


Front End Command Queuing

FRONT

END

FRONT

END

Request 1

Request 2

Request 3

Request 4

1234

FRONT

END

FRONT

END

Request 1

Request 2

Request 3

Request 4

1324

Without Command Queuing

With Command Queuing

1

2

34

1

2

34


Intelligent Storage System: Cache


Host Connectivity

Front End Back End

Cache

Physical Disks


Intelligent Storage System: Back End

Host Connectivity

PortsControllers

Front End Back End

Cache

Physical Disks



Intelligent Storage System: Physical Disks

Host Connectivity

Front End Back End

Cache

Physical Disks



What the Host Sees – Physical Drive Partitioning


LUN 0LUN 1LUN 2

LUN 0

LUN 1

LUN 2

Host

Host

Back EndPhysical Disks

Cache


What the Host Sees – RAID Sets and LUNs


LUN 0

LUN 1

Host

Host

LUN 0

LUN 1

Back End Physical Disks

Cache


Logical Device Names

HostVolumeManager

Host

/dev/rdsk/c1t1d0

/dev/rdsk/c1t1d1

\\.\PhysicalDrive0

VolumeManager


LUN 0LUN 1LUN 2

LUN 0

LUN 1

LUN 2

Back EndPhysical Disks

Cache


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


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


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

CacheRead

RequestWrite

Request

Acknowledgment


How Cache is Structured

Data Store

Tag RAM



ReadRequest

Read Cache ‘Hits’ and ‘Misses’

CacheRead

Request

Cache

Data found in cache = ‘Hit’

No data found = ‘Miss’


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


WriteRequest

Write Algorithms

WriteRequest

Write-through Cache

Write-back

Acknowledgement

Acknowledgement

Cache

Cache

Acknowledge-ment


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


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


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


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?


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


CLARiiON CX3-80 Architecture

Power supply

Power supply

Fan FanFan

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

UltraScaleStorage Processor

UltraScaleStorage Processor

Fibre Channel

Mirrored cache

Fibre Channel

CPU

Mirrored cache

CPU

FC FC

CPU

FC

CPU

FCFC FC FCFC

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


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


EMC Symmetrix DMX Array

Direct Matrix Interconnect

Dynamic Global Memory

Enginuity Operating Environment

Processing Power

Flexible Back-End Configurations

Fault-tolerant Design


Symmetrix DMX Series Direct Matrix Architecture


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 DriveS= Secondary Connection for Redundancy


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


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 AddressTarget = 1LUN = 0

Hyper

Volumes


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


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

Documents

Disk Storage Systems