© 2009 emc corporation. all rights reserved. intelligent storage systems module 1.4

© 2009 EMC Corporation. All rights reserved.

Intelligent Storage SystemsIntelligent Storage Systems

Module 1.4

© 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 2

Module Objectives

After completing this module, you will be able to:

Describe components of intelligent storage system

List benefits of intelligent storage system

Explain intelligent cache algorithms and protection

Describe intelligent storage array implementation – High-end storage array

– Mid-range storage array


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

– 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 (JBOD) or even a RAID arrays:– Increased capacity

– Improved performance

– Easier data management

– Improved data availability and protection

– Enhanced Business Continuity support

– Improved security and access control


Components of an Intelligent Storage System

Host

Connectivity

FC SAN

Front End Back End

Cache

Physical Disks

Intelligent Storage System


Intelligent Storage System: Front End

Host

Connectivity

Front End Back End

Cache

Physical Disks


FC SAN

Ports Controllers


Front End Command Queuing

D C B AD C B A

A

B

C DI/O Requests I/O Processing

Order

Front-End Controller

Cylinders

Without Optimization (FIFO)

D B C AD C B A

A

B

C DI/O Requests I/O Processing

Order

Front-End Controller

Cylinders

With command queuing


Disk Scheduling

The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth.

Access time has two major components– Seek time is the time for the disk are to move the heads to the cylinder

containing the desired sector.

– Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.

Minimize seek time

Seek time seek distance

Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer.


Disk Scheduling (Cont.)

Several algorithms exist to schedule the servicing of disk I/O requests.

We illustrate them with a request queue (0-199).

98, 183, 37, 122, 14, 124, 65, 67

Head pointer 53


FCFS (First Come, First Served)

Illustration shows total head movement of 640 cylinders.


SSTF (Shortest Seek Time First)

Selects the request with the minimum seek time from the current head position.

SSTF scheduling is a form of SJF (Shortest Job First) scheduling; may cause starvation of some requests.



SSTF (Cont.)

65, 67, 37, 14, 98, 122, 124, 183


SCAN

The disk arm starts at one end of the disk, and moves toward the other end, servicing requests until it gets to the other end of the disk, where the head movement is reversed and servicing continues.

Sometimes called the elevator algorithm.



SCAN (Cont.)

37, 14, 65, 67, 98, 122, 124, 183


C-SCAN (Circular-SCAN)

Provides a more uniform wait time than SCAN.

The head moves from one end of the disk to the other. servicing requests as it goes. When it reaches the other end, however, it immediately returns to the beginning of the disk, without servicing any requests on the return trip.

Treats the cylinders as a circular list that wraps around from the last cylinder to the first one.


C-SCAN (Cont.)

65, 67, 98, 122, 124, 183, 14,37


C-LOOK

Version of C-SCAN

Arm only goes as far as the last request in each direction, then reverses direction immediately, without first going all the way to the end of the disk.


C-LOOK (Cont.)

65, 67, 98, 122, 124, 183, 14,37


Selecting a Disk-Scheduling Algorithm

SSTF is common and has a natural appeal.

SCAN and C-SCAN perform better for systems that place a heavy load on the disk.

Performance depends on the number and types of requests.

Requests for disk service can be influenced by the file-allocation method.

The disk-scheduling algorithm should be written as a separate module of the operating system, allowing it to be replaced with a different algorithm if necessary.

Either SSTF or LOOK is a reasonable choice for the default algorithm.


Intelligent Storage System: Cache

Host

Connectivity

Front End Back End

Cache

Physical Disks


FC SAN


WriteRequest

Write Operation with Cache

WriteRequest

Write-through Cache

Write-back

Acknowledgement

Acknowledgement

Cache

Cache

Acknowledgement


ReadRequest

CacheRead

Request

Cache

Data found in cache = ‘Hit’

No data found = ‘Miss’

Read Operation with Cache: ‘Hits’ and ‘Misses’


Cache Management: Algorithms

Least Recently Used (LRU)– Discards least recently used data

Most Recently Used (MRU)– Discards most recently used data

New Data

Oldest Data


Cache Management: Watermarking

LWM

HWM

100 %

Idle flushing High watermark flushing Forced flushing

Manage peak I/O requests “bursts” through flushing/de-staging– Idle flushing, High Watermark flushing and Forced flushing

For maximum performance:– Provide headroom in write cache for I/O bursts


Cache Data Protection

Protecting cache data against failure:– Cache mirroring

Each write to the cache is held in two different memory locations on two independent memory cards

– Cache vaulting Cache is exposed to the risk of uncommitted data loss due to power

failure


Intelligent Storage System: Back End

Host

Connectivity

PortsControllers

Front End Back End

Cache

Physical Disks


FC SAN


Intelligent Storage System: Physical Disks

Host

Connectivity

Front End Back End

Cache

Physical Disks


FC SAN


What the Host Sees – RAID Sets and LUNs

Host 1

Host 2

LUN 0

LUN 1

Front End Back End

Cache

Physical Disks


LUN 0

LUN 1

Connectivity

FC SAN


LUN Masking

LUN masking is access control mechanism

Process of masking LUNs from unauthorized access

Implemented on storage arrays

Storage group logical entity that contains one or more LUNs and one host


ISS Implementation: High-end Storage Systems

Also referred as Active-active arrays– I/O’s are serviced through all the available

paths

Following are high-end array capabilities:– Large storage capacity

– Huge cache to service host I/Os

– Fault tolerance architecture

– Multiple front-end ports and support to interface protocols

– High scalability

– Ability to handle large amounts of concurrent I/Os

Designed for large enterprises

HostStorage

Array

Active-Active Configuration

Active

Active

LUN

Co

ntr

oll

er

AC

on

tro

ller

B

Port

Port


Midrange Storage Systems

Also referred as Active-passive arrays– Host can perform I/Os to LUNs only

through active paths

– Other paths remain passive till active path fails

Midrange array have two controllers, each with cache, RAID controllers and disks drive interfaces

Designed for small and medium enterprises

Less scalable as compared to high-end array

HostStorage

Array

Active-Passive Configuration

Active

Passive

LUN

Co

ntr

oll

er

AC

on

tro

ller

B

Port

Port


Module Summary

Key points covered in this module:

Intelligent Storage Systems features

Components of Intelligent Storage Systems

Cache management algorithms

Intelligent Storage System implementation– High-end storage array

– Mid range storage array


Concept in Practice: EMC CLARiiON Support for UltraFlex technology

Scalable from up to 960 disks

Supports flash drives

Supports different types and sizes of drives, and RAID types (0, 1, 1+0, 3, 5, 6)

Supports up to 16 GB of available cache memory per controller (Storage Processor)

Enhances availability with non disruptive upgrade and failover

Ensures data protection through mirrored write cache and cache vaulting

Supports storage-based local and remote data replication – Through SnapView and MirrorView software


CPU CPU CPU CPU

CPU CPU CPU CPU

Memory

CPU Module

Multi-Core Processors

FC Module

I/O Complex

FC Module

FC Module

FC Module

iSCSI Module

iSCSI Module

4 Gb/s Fibre

Channel Back-End

CLARiiON Messaging Interface (CMI)

Multi-Lane PCI-Express Bridge Link

Power Supply SPS

SPS

Fan Fan Fan Fan

Power Supply

4 Gb/s Fibre

Channel Back-End4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s LCC

4 Gb/s Fibre Channel Front-End CPU CPU CPU CPU

CPU CPU CPU CPU

Memory

CPU Module

Multi-Core Processors

FC Module

I/O Complex

FC Module

FC Module

FC Module

iSCSI Module

iSCSI Module

Storage Processor Storage Processor

CLARiiON CX-4 Architecture


EMC Symmetrix Incrementally scalable to 2,400 disks

Supports Flash-based solid-state drives

Dynamic global cache memory (16 GB–512 GB)

Advanced processing power (up to 130 PowerPC)

Direct matrix Architecture

High data processing bandwidth (up to 128 GB/s)

Data protection with RAID 1, 1+0 (also known as 10 for mainframe), 5, and 6

Storage-based local and remote replication – Through TimeFinder and SRDF software


Direct Matrix Architecture

FC (Back-End)

DirectMatrix

DirectMatrix

Cntl

FC (Back-End)

DirectMatrix

DirectMatrix

Cntl

FC (BE or FE)

DirectMatrix

DirectMatrix

Cntl

FC (BE or FE)

DirectMatrix

DirectMatrix

Cntl

FC (BE or FE)

DirectMatrix

DirectMatrix

Cntl

FC (BE or FE)

DirectMatrix

DirectMatrix

Cntl

FC (Back-End)

DirectMatrix

DirectMatrix

Cntl

FC (Back-End)

DirectMatrix

DirectMatrix

Cntl

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

A

A

B

B

ESCON Director

DirectMatrix

DirectMatrix

Cntl

ESCONhost attach

FC Director

DirectMatrix

DirectMatrix

Cntl

Fibre Channelhost attach

Multi-Protocol CD

DirectMatrix

DirectMatrix

Cntl

FICON, GigE, iSCSIhost attach

Multi-Protocol CD

DirectMatrix

DirectMatrix

Cntl


Multi-Protocol CD

DirectMatrix

DirectMatrix

Cntl


Multi-Protocol CD

DirectMatrix

DirectMatrix

Cntl


FC Director

DirectMatrix

DirectMatrix

Cntl

Fibre Channelhost attach

ESCON Director

DirectMatrix

DirectMatrix

Cntl

ESCONhost attach

SymmetrixFibre Channel disk devices


Fibre Channelback-enddirector *





SymmetrixFibre Channeldisk devices

Battery backupUnit Modules

Cooling

Environmentalcontrol and

status signals

Environmentalcontrol and

status signals

64 GBMemory

64 GBMemory

64 GBMemory

64 GBMemory

64 GBMemory

64 GBMemory

64 GBMemory

64 GBMemory

Control and communications Signals

Control and communications Signals

Power supplies

ModemService

Processor

UPS


Check Your Knowledge

What are the parts of an Intelligent Storage System?

What are the differences between a high-end and midrange storage 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?

© 2009 emc corporation. all rights reserved. intelligent storage systems module 1.4

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