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RAID Arrays RAID Arrays

RAID Arrays - PowerPoint Presentation

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RAID Arrays - PPT Presentation

Redundant Array of Inexpensive Discs What is RAID Arrays RAID is an acronym for Redundant Array of Independent Drives or Disks also known as Redundant Array of Inexpensive Drives or Disks The various types of RAID are data storage schemes that divide andor replicate data among multiple ha ID: 379131

block raid data arrays raid block arrays data parity array disk controller disks host drives striped independent mirroring drive

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Slide1

RAID Arrays

Redundant Array of Inexpensive DiscsSlide2

What is RAID Arrays?

RAID is an acronym for Redundant Array of Independent Drives (or Disks), also known as Redundant Array of Inexpensive Drives (or Disks)

The various types of RAID are data storage schemes that divide and/or replicate data among multiple hard drivesSlide3

Why Use RAID?

Improved Reliability

Improved Performance

Fault Tolerance

Improved Availability

Higher Data SecuritySlide4

Key Terms

Mirroring

- the copying of data to more than one disk

Striping

- the splitting of data across more than one disk

Parity

- a redundancy check that ensures that the data is protected without having to have a full set of duplicate drives.

Duplexing - an extension of mirroring that is based on the same principle as that technique expect it goes one step further in that it also duplicates the hardware that controls the two hard drives (or sets of hard drives).

RAID ArraysSlide5

RAID - Redundant Array of Independent Disks

RAID Arrays

RAID

Controller

RAID Array

HostSlide6

RAID Components

RAID Arrays

RAID

Controller

Logical Array

Logical Array

Physical Array

RAID Array

HostSlide7

Data Organization: Strips and Stripes

RAID Arrays

Stripe 1

Stripe 2

Stripe 3

StripsSlide8

RAID Levels

0 Striped array with no fault tolerance

1 Disk mirroring

3 Parallel access array with dedicated parity disk

4 Striped array with independent disks and a dedicated parity disk

5 Striped array with independent disks and distributed parity

6 Striped array with independent disks and dual distributed parity

Combinations of levels (I.e., 1 + 0, 0 + 1, etc.)RAID ArraysSlide9

RAID 0

A striped set of at least two disks without parity

The data is broken down into blocks and each block is written to a separate disk drive

Best performance is achieved when data is striped across multiple controllers with only one drive per controller Slide10

RAID 0 – Striped Array with no Fault Tolerance

RAID Arrays

-

10

RAID

Controller

Block 4

Block 4

Block 3

Block 3

Block 2

Block 2

Block 1

Block 1

Block 0

Block 0

HostSlide11

Advantages of RAID 0

I/O performance is greatly improved by spreading the I/O load across many channels and drives

No parity calculation overhead is involved

Very simple design

Easy to implement Slide12

Disadvantages of RAID 0

Not a "True" RAID because it is NOT fault-tolerant

The failure of just one drive will result in all data in an array being lost

Should never be used in mission critical environments Slide13

RAID 1 – Disk Mirroring

RAID Arrays

-

13

RAID

Controller

Block 1

Block 1

Block 1

Block 0

Block 0

Block 0

HostSlide14

RAID 1 Advantages

High data availability and high I/O rate (small block size).

Improves read performance - twice the read transaction rate of single disks, same write transaction rate as single disks

100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk

Simplest RAID storage subsystem design – easy to maintainSlide15

RAID 1 Disadvantages

Expensive due to the extra capacity required to duplicate data. Overhead cost equals 100%, while usable storage capacity is 50%.

May not support hot swap of failed disk when implemented with software. Use hardware implementation.Slide16

RAID 0+1 – Striping and Mirroring

RAID Arrays

RAID

Controller

Block 3

Block 3

Block 3

Block 2

Block 2

Block 2

Block 1

Block 1

Block 1

Block 0

Block 0

Block 0

HostSlide17

RAID 1+0 – Mirroring and Striping

RAID Arrays

RAID

Controller

Block 3

Block 3

Block 3

Block 2

Block 2

Block 2

Block 1

Block 1

Block 1

Block 0

Block 0

Block 0

HostSlide18

RAID 0+1 vs. RAID 1+0

Benefits are identical under normal operations

Rebuild operations are very different

RAID 1+0 uses a mirrored pair – only 1 disk is rebuilt if a disk fails

RAID 0+1 if a single drive fails, the entire stripe is faulted

RAID is 0+1 is a poorer solution and is less common

RAID ArraysSlide19

RAID Redundancy: Parity

-

19

RAID Arrays

Parity Disk

0

8

4

1

9

5

2

10

6

3

11

7

0 1 2 3

8 9 10 11

4 5 6 7

RAID

Controller

HostSlide20

Parity Calculation

RAID Arrays

Parity

Data

Data

Data

Data

4

2

3

5

14

5 + 3 + 4 + 2 = 14

The middle drive fails:

5 + 3 + ? + 2 = 14

? = 14 – 5 – 3 – 2

? = 4

RAID ArraySlide21

RAID 3 – Parallel Transfer with Dedicated Parity Disk

RAID Arrays

RAID

Controller

Block 1

Block 2

Block 3

P 0 1 2 3

Block 0

Block 3

Block 2

Block 1

Block 0

Parity

Generated

HostSlide22

RAID 4 – Striping with Dedicated Parity Disk

RAID Arrays

RAID

Controller

P 0 1 2 3

Block 0

Block 0

Block 0

Block 4

Block 1

Block 5

Block 2

Block 6

Block 3

Block 7

P 0 1 2 3

P 4 5 6 7

Parity

Generated

Block 0

P 0 1 2 3

HostSlide23

RAID 5 – Independent Disks with Distributed Parity

RAID Arrays

Block 0

P 0 1 2 3

Block 7

RAID

Controller

P 0 1 2 3

Block 0

Block 4

Block 0

Block 1

Block 5

Block 2

Block 6

Block 3

Parity

Generated

Block 0

P 0 1 2 3

Block 4

P 4 5 6 7

P 4 5 6 7

Block 4

P 4 5 6 7

Block 4

Parity

Generated

HostSlide24

RAID 6 – Dual Parity RAID

Two disk failures in a RAID set leads to data unavailability and data loss in single-parity schemes, such as RAID-3, 4, and 5

Increasing number of drives in an array and increasing drive capacity leads to a higher probability of two disks failing in a RAID set

RAID-6 protects against two disk failures by maintaining two parities

Horizontal parity which is the same as RAID-5 parity

Diagonal parity is calculated by taking diagonal sets of data blocks from the RAID set members

Even-Odd, and Reed-Solomon are two commonly used algorithms for calculating parity in RAID-6

RAID ArraysSlide25

RAID Implementations

Hardware (usually a specialized disk controller card)

Controls all drives attached to it

Performs all RAID-related functions, including volume management

Array(s) appear to the host operating system as a regular disk drive

Dedicated cache to improve performance

Generally provides some type of administrative software

Software Generally runs as part of the operating system Volume management performed by the serverProvides more flexibility for hardware, which can reduce the costPerformance is dependent on CPU loadHas limited functionality

RAID ArraysSlide26

Hot Spares

RAID Arrays

RAID

ControllerSlide27

Hot Swap

RAID Arrays

RAID

Controller

RAID

Controller

RAID

ControllerSlide28

Check Your Knowledge

What is a RAID array?

What benefits do RAID arrays provide?

What methods can be used to provide higher data availability in a RAID array?

What is the primary difference between RAID 3 and RAID 5?

What is a hot spare?

RAID Arrays