Introduction To RAIDIntroduction To RAID

RAID RAID

Redundant Array Of Independent Disks

• Standard RAID levels – RAID 0 to RAID 6

• Nested RAID levels - Striped Mirrors RAID 1+0

RAID - 0RAID - 0• 4 Disk Drives

• Stripe size = 16 KB

• Red File = 4 KB • • Green File = 100 KB

• Magenta File = 500 KB

• 2 Disk Drives

• Red File = 4 KB • Green File = 100 KB

• Magenta File = 500 KB

RAID - 1RAID - 1

Disks are MIRRORED

RAID - 2RAID - 2

• Data is split into bits

• The bits are written into several disks in parallel.

• The ECC (Error Correcting Codes) are also computed each time a read or write is performed and the ECC codes are written or read from the separate set of disks.

• Data is striped at bit level

•Several disks are required for storing Error Correcting codes.

RAID - 3RAID - 3

• 4 Disk Drives

• Stripe size = 1 bit

• Red File = 4 KB

• Green File = 100 KB

• Magenta File = 500 KB

• Data is striped at bit level

•One Dedicated PARITY Disk

RAID - 4RAID - 4

• 4 Disk Drives

• Stripe size = 16 KB

• Red File = 4 KB

• Green File = 100 KB

• Magenta File = 500 KB

Block-Interleaved Parity

• Data is striped at block level

•One Dedicated PARITY Disk

RAID - 5RAID - 5Block-level striping with distributed parity.

• 4 Disk Drives

• Stripe size = 16 KB

• Red File = 4 KB

• Green File = 100 KB

• Magenta File = 500 KB

• Data is striped at block level

•PARITY is distributed across disks

RAID - 6RAID - 6Block-level striping with dual distributed

parity.

• 4 Disk Drives

• Stripe size = 16 KB

• Red File = 4 KB

• Green File = 100 KB

• Magenta File = 500 KB

• Data is striped at block level

•2 sets of parity information

•PARITY is distributed across disks

•Can protect up to 2 disk failures

RAID 5 vs. RAID - 6RAID 5 vs. RAID - 6Parameters RAID - 5 RAID - 6

Performance Better Worse

Cost Higher Lower

Fault Tolerance

Lower Higher

• Industry Standard – RAID 5

•REASONS –

• Cost of RAID 6 is very HIGH• The probability of two disk failure at the same time is very low.

RAID 0 + 1RAID 0 + 1Mirrored Striping

• 4 Disk Drives

• Stripe size = 16 KB

• Red File = 4 KB • Green File = 100 KB

• Magenta File = 500 KB

IntroductionIntroduction

SCSI SCSI

&&

Fiber Channel Fiber Channel

A Few Storage Basics….A Few Storage Basics…. Where will data finally end up?Where will data finally end up? How will it get there?How will it get there?

What will it pass through?What will it pass through?

Direct Attached Storage Direct Attached Storage (Internal)(Internal)

Computer System

CPU

Memory

Bus

I/O - RAID Controller

Disk Drives

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DAS with internal controller DAS with internal controller and external storageand external storage

CPU

Memory

Bus

I/O - RAID Controller

Computer System

Disk Drives

Disk Drives

Disk Drives

Disk Enclosure

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Comparing Internal and Comparing Internal and External StorageExternal Storage

Internal Storage

Server

Storage

RAID controllers and disk drives are internal to the server

SCSI, ATA, or SATA protocol between controller and disks

SCSI Bus with external storage

Server

RAID Controller

Storage

RAID Controller

Disk Drives

RAID controller is internal

SCSI or SATA protocol between controller and disks

Disk drives are external

Disk Drives

DAS with external controller DAS with external controller and external storageand external storage

Computer System

CPU

Memory

Bus

HBA

RAIDController

Storage System

Disk Drives

Disk Drives

Disk Drives

Disk Enclosure12345

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DAS over Fibre ChannelDAS over Fibre ChannelServer

HBA

Storage

Disk drives and

RAID controller are external

Disk Drives

RAID Controller

HBA is internal

Fibre Channel protocol between HBAs and external RAID controller

External SAN Array

I/O TransferI/O Transfer RAID ControllerRAID Controller

Contains the LOGICContains the LOGIC Determines how the data will be written Determines how the data will be written

(striping, mirroring, RAID 10, RAID 5, etc.)(striping, mirroring, RAID 10, RAID 5, etc.)

Host Bus Adapter (HBA)Host Bus Adapter (HBA) Simply transfers the data to the RAID Simply transfers the data to the RAID

controller. controller. Doesn’t do any RAID or striping calculations. Doesn’t do any RAID or striping calculations. ““Dumb” for speed.Dumb” for speed. Required for external storage.Required for external storage.

Fibre Channel: What is it?Fibre Channel: What is it?

Fibre Channel is a network protocol Fibre Channel is a network protocol implemented specifically for implemented specifically for dedicated storage networksdedicated storage networks

Fibre Channel utilizes specializedFibre Channel utilizes specialized SwitchesSwitches Host Bus AdaptersHost Bus Adapters RAID controllersRAID controllers CablesCables

switch

Fibre Channel Fibre Channel ComponentsComponents

RAID Controller RAID Controller

switch

ServersServers Host Bus AdaptersHost Bus Adapters

CablesCables Fiber optic or copperFiber optic or copper

Fibre Channel SwitchesFibre Channel Switches Two switches for Two switches for

redundancyredundancy Fibre Channel Storage Fibre Channel Storage

ArrayArray Two RAID Controllers for Two RAID Controllers for

redundancyredundancy 4–100+ disk drives per 4–100+ disk drives per

arrayarray A true storage networkA true storage network

Multiple serversMultiple servers Multiple switchesMultiple switches Multiple Storage ArraysMultiple Storage Arrays

Server A

HBA

Server B

HBA

Server C

HBA

Disk Drives

FC Storage Array

HBA HBA HBA

SAN & Fibre ChannelSAN & Fibre Channel

Storage Area NetworkStorage Area Network

A network whose primary purpose is the A network whose primary purpose is the transfer of data between storage systems transfer of data between storage systems and computer systemsand computer systems

Fibre Channel is the primary technology Fibre Channel is the primary technology utilized for SANsutilized for SANs

Recently, SANs have been implemented Recently, SANs have been implemented with dedicated iSCSI networkswith dedicated iSCSI networks

SAN & Fibre ChannelSAN & Fibre Channel

Fibre Channel TechnologyFibre Channel Technology Provides concurrent communications between Provides concurrent communications between

servers, storage devices, and other peripheralsservers, storage devices, and other peripherals

A gigabit interconnect technologyA gigabit interconnect technology

A highly reliable interconnectA highly reliable interconnect

Up to 127 devices (SCSI: 15)Up to 127 devices (SCSI: 15)

Up to 10 km of cabling (3-15 ft. for SCSI)Up to 10 km of cabling (3-15 ft. for SCSI)

Physical interconnect can be copper or fiber opticPhysical interconnect can be copper or fiber optic

Fibre Channel – Fibre Channel – (continued)(continued) Hot-pluggable - Devices can be removed or Hot-pluggable - Devices can be removed or

added at will with no ill effects to data added at will with no ill effects to data communicationscommunications

Provides a data link layer above the physical Provides a data link layer above the physical interconnect, analogous to Ethernetinterconnect, analogous to Ethernet

Sophisticated error detection at the frame levelSophisticated error detection at the frame level

Data is checked and resent if necessaryData is checked and resent if necessary

Fibre Channel – Frame Fibre Channel – Frame DissectionDissection

Up to 2048 byte Up to 2048 byte payloadpayload

4 byte 4 byte checksum for checksum for each frameeach frame

SCSI Commands

Fibre Channel Interface Fibre Channel Interface LayersLayers

Device Driver

SCSI Protocol

Fibre Channel

Fiber Optic or Copper Cabling

SCSI vs. Fibre ChannelSCSI vs. Fibre ChannelProtocolProtocol SCSISCSI

SCSI is an established, tried and true protocolSCSI is an established, tried and true protocol Supported in every major OS on marketSupported in every major OS on market

Fibre ChannelFibre Channel Fibre Channel runs on top of SCSIFibre Channel runs on top of SCSI No re-inventing the wheelNo re-inventing the wheel Immediate OS supportImmediate OS support

SCSI SCSI vs. vs. Fibre Fibre ChannelChannel

Interface for internal storage to external disks

Potential down time with SCSI

Single bus

RAID controller is SCSI hardware

Standards: Ultra2 (80 MB/sec) Ultra 160 (160 MB/sec) Ultra 320 (320 MB/sec)

Media specific (copper only)

SCSI Limitations: Cables can’t be any longer

than 3 feet for single ended; 15 feet for LVD (low voltage differential)

No more than 15 devices on a SCSI bus

Used with SAN

Lots of built-in redundancy with connections

Redundant network

HBA is fibre channel hardware

Standards: 1 Gbps to 10 Gbps

Provides a data link layer above the physical interconnect Analogous to Ethernet FC is a network of devices It can be media independent-

copper or fiber optic

Fibre Channel limitations: Cable length: Up to 10 kilometers

(more a limitation of cable than FC itself)

Up to 127 devices

FC Network

User

Server

FC Frame FC Frame

RAIDController Storage

Device

11 User issues a request for data to a local server

22 The SCSI command is encapsulated in FC protocol & transmitted

over FC Network

33 The packet is decapsulatedseparating the SCSI commands

44The SCSI commands are received by the

Internal SCSI Controller, and the data is retrieved.

55The data request is again encapsulated in FC

Protocol then returned

HBA

SCSI & FC in SANSCSI & FC in SAN

Fibre TopologiesFibre Topologies

Point-to-pointPoint-to-point

Only two FC devices Only two FC devices connected directly connected directly togethertogether

No sharing of media - No sharing of media - devices each benefit devices each benefit from total link from total link bandwidth bandwidth

Fibre TopologiesFibre Topologies

Arbitrated LoopArbitrated Loop

127 addresses or 126 127 addresses or 126

devices per loopdevices per loop

Blocking, shared mediaBlocking, shared media

100MB/sec speed.100MB/sec speed.

Lowest cost Fibre Lowest cost Fibre

protocolprotocol

Fibre TopologiesFibre Topologies

Switched FabricSwitched Fabric

Connect millions of devices Connect millions of devices

Non-shared media Non-shared media

200MB/sec between nodes200MB/sec between nodes

Data rates for various SCSI Data rates for various SCSI interfaces interfaces

InterfaceWidth(bits)

Clock

Maximum

Throughput (MB/s)

Throughput (Mbit/s)

Length Devices

SSA 1 200 MHz 40 MB/s 320 Mbit/s 25 m 96

SSA 40 1 400 MHz 80 MB/s 640 Mbit/s 25 m 96

FC-AL1Gb 1 1 GHz 100 MB/s 800 Mbit/s 500m/3 km 127

FC-AL 2Gb 1 2 GHz 200 MB/s 1600 Mbit/s 500m/3 km 127

FC-AL 4Gb 1 4 GHz 400 MB/s 3200 Mbit/s 500m/3 km 127

SAS 1 3 GHz 300 MB/s 2400 Mbit/s 6 m 16,256

iSCSI Implementation- and network-dependent

THANK YOU

DAS - ScalabilityDAS - Scalability

Limited to the servers predetermined capacity

External expansion with SCSI is limited to 15 devices per channel12M Distance limitation

Expensive, disruptive to scale

High management costs

Still has over/under utilisation issues

SAN BenefitsSAN Benefits

Grows storage independently of servers

Centralized high-availability storage reduces storage management overhead

Scalable - Supports thousands of interconnected devices

High aggregate bandwidth, multiple paths

2Gig, 4Gig fibre, Gigabit Ethernet

Application clustering possible on wider scale

Disaster Recovery