What is RAID? Benefits of RAID Concepts of RAID RAID

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CPEG323 1 OVERVIEW What is RAID? Benefits of RAID Concepts of RAID RAID Levels

description

All about RAID

Transcript of What is RAID? Benefits of RAID Concepts of RAID RAID

Page 1: What is RAID? Benefits of RAID Concepts of RAID RAID

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OVERVIEW

What is RAID?

Benefits of RAID

Concepts of RAID

RAID Levels

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RAID AND ITS BENEFITS

What is RAID?

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks.

Benefits OF RAID Improved Performance High Availability Fault Tolerance

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RAID CONCEPTS

STRIPING

MIRRORING

PARITY

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RAID Concepts(Striping)

                                                                                                                                   

                                                                                                                                   

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Raid Concepts (Mirroring)

All data in the system is written simultaneously to two hard disks instead of one; thus the "mirror" concept .

100% data redundancy which provides full protection against the

failure of either of the disks containing the duplicated data.

                                                                   

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RAID Concepts(Parity)

Parity is redundancy information calculated from the actual data values.

take "N" pieces of data, and from them, compute an extra piece of data. Take the "N+1" pieces of data and store them on "N+1" drives. If you lose any one of the "N+1" pieces of data, you can recreate it from the "N" that remain, regardless of which piece is lost.

The parity calculation is typically performed using a logical operation called "exclusive OR" or "XOR".

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RAID LEVELS

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RAID: Level 0 (No Redundancy; Striping)

Multiple smaller disks as opposed to one big disk Spreading the blocks over multiple disks – striping – means that

multiple blocks can be accessed in parallel increasing the performance .

A 3 disk system gives 3 times the throughput of a 1 disk system

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RAID: Level 0 (No Redundancy; Striping)

No redundancy, so what if one disk fails? Failure of one or more disks results in data loss.

RECOMMENDED APPLICATIONS

Video Production and Editing Image Editing Any application requiring high bandwidth

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RAID: Level 1 (Redundancy via Mirroring)

Uses twice as many disks as RAID 0 (e.g., 8 smaller disks with second set of 4 duplicating the first set) so there are always two copies of the data

# redundant disks = # of data disks so twice the cost of one big disk

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RAID: Level 1 (Redundancy via Mirroring)

What if one disk fails? If a disk fails, the system just goes to the “mirror” for the data

Recommended Application

Accounting

Payroll

Financial

Any application requiring very high availability

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RAID: Level 2 (Redundancy via ECC)

ECC disks contain the parity of data on a set of distinct overlapping disks

# redundant disks = log (total # of data disks) so almost twice the cost of one big disk

- writes require computing parity to write to the ECC disks

- reads require reading ECC disk and confirming parity

Can tolerate limited disk failure, since the data can be reconstructed

blk1,b0 blk1,b2blk1,b1 blk1,b3Checks 4,5,6,7

Checks 2,3,6,7

Checks 1,3,5,7

3 5 6 7 4 2 1

10 0 0 11

ECC disks

0

ECC disks 4 and 2 point to either data disk 6 or 7, but ECC disk 1 says disk 7 is okay, so disk 6 must be in error

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RAID: Level 3 (Bit-Interleaved Parity)

On RAID 3 systems, data blocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array.

writes require writing the new data to the data disk as well as computing the parity, meaning reading the other disks, so that the parity disk can be updated

Can tolerate limited disk failure, since the data can be reconstructed

reads require reading all the operational data disks as well as the parity disk to calculate the missing data that was stored on the failed disk

blk1,b0 blk1,b2blk1,b1 blk1,b3

10 01

(odd)bit parity disk

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RAID: Level 3 (Bit-Interleaved Parity)

On RAID 3 systems, data blocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array.

writes require writing the new data to the data disk as well as computing the parity, meaning reading the other disks, so that the parity disk can be updated

Can tolerate limited disk failure, since the data can be reconstructed

reads require reading all the operational data disks as well as the parity disk to calculate the missing data that was stored on the failed disk

blk1,b0 blk1,b2blk1,b1 blk1,b3

10 0 1

(odd)bit parity diskdisk fails

1

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RAID: Level 3 (Bit-Interleaved Parity)

Recommended Applications

Video Production and live streaming

Image Editing

Video Editing

Any application requiring high throughput

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RAID: Level 4 (Block-Interleaved Parity)

RAID 4 improves performance by striping data across many disks in blocks, and provides fault tolerance through a dedicated parity disk.

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RAID: Level 4 (Block-Interleaved Parity)

It is like RAID 3 except that it uses blocks instead of bytes for striping

Supports “small reads” and “small writes” (reads and writes that go to just one (or a few) data disk)

by watching which bits change when writing new information, need only to change the corresponding bits on the parity disk

the parity disk must be updated on every write, so it is a bottleneck for back-to-back writes

Can tolerate limited disk failure, since the data can be reconstructed

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Small Writes RAID 3 small writes

New D1 data

D1 D2 D3 D4 P

D1 D2 D3 D4 P

3 reads and

2 writes involving all

the disks

RAID 4 small writesNew D1 data

D1 D2 D3 D4 P

D1 D2 D3 D4 P

2 reads and 2 writes

involving just two disks

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RAID: Level 5 (Distributed Block-Interleaved Parity)

Parity is distributed across the disks Supports “small reads” and “small writes” (reads and writes that

go to just one (or a few) data disk) Allows multiple simultaneous writes as long as the

accompanying parity blocks are not located on the same disk

Can tolerate limited disk failure, since the data can be reconstructed

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RAID: Level 5 (Distributed Block-Interleaved Parity)

Recommended Applications

File and Application servers

Database servers

Web, E-mail, and News servers

Intranet servers

Most versatile RAID level

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Distributing Parity Blocks

By distributing parity blocks to all disks, some small writes can be performed in parallel

1 2 3 4 P0

5 6 7 8 P1

9 10 11 12 P2

13 14 15 16 P3

RAID 4 RAID 5

1 2 3 4 P0

5 6 7 P1 8

9 10 P2 11 12

13 P3 14 15 16

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Raid : Level 6

RAID level 6 is an evolution of RAID 5. RAID 6 uses double parity for additional fault tolerance.

Like in RAID 5, data is striped at a block level across the disk sets while parity information is generated and written across the array. Now it's possible for more than one drive to fail simultaneously, and the RAID will still operate.

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RAID: Level 6

Advantages Perfect solution for mission critical applications as it can sustain

multiple drive failures .

Disadvantages Uses 2 drives for parity

Recommended Applications Database server Mail server Web server Intranet server Transaction processing

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RAID: Level 0+1 (Striping with Mirroring)

Combines the best of RAID 0 and RAID 1, data is striped across four disks and mirrored to four disks

Four times the throughput (due to striping) # redundant disks = # of data disks so twice the cost of one big

disk

writes have to be made to both sets of disks, so writes would be only 1/2 the performance of RAID 0

blk1 blk3blk2 blk4 blk1 blk2 blk3 blk4

redundant (check) data

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RAID: Level 0+1 (Striping with Mirroring)

What if one disk fails? If a disk fails, the system just goes to the “mirror” for the data

Recommended Applications

Imaging applications

General fileserver

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RAID: Level 1+0 (Mirroring with Striping)

RAID Level 10 provides very high performance and redundancy. 

Data is simultaneously mirrored and striped.  Can under circumstances support multiple drive failures.

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THANK YOU

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