RAID and Its Levels

Presented By:

Hassan Mehmood

2419

Semester:

7th(BS.IT)

Define:

Raid stands for Redundant array of inexpensive/ independent disks.

“It is a data storage virtualization technology that combines multiple disk drive components into a logical unit for the purposes of performance improvement.”

Raid Levels:

1. Raid 0 2. Raid 1 3. Raid 2

4. Raid 3 5. Raid 4 6. Raid 5

7. Raid 6

What is RAID

Why we need Raid

Computing speeds double every 3 years

Disk speeds can’t keep up

I/O Performance and Availability Issues!

Raid allows us to avoid those issues by,

1.Parallelism

2.Load Balancing

3.Redundancy: Mirroring, or Striping with Parity

4.Availability/Cost

Mirroring

Keep to copies of data on two separate disks

Gives good error recovery

if some data is lost, get it from the other source

Expensive

requires twice as many disks

Write performance can be slow

have to write data to two different spots

Read performance is enhanced

can read data from file in parallel

Same data written to both disks.

Striping

Take file data and map it to different disks

Allows for reading data in parallel

file data block 1block 0 block 2 block 3

Disk 0 Disk 1 Disk 2 Disk 3

Raid 0:

It splits data evenly across two

Or more disks. RAID 0 is normallyused to increase performance,

although it can also be used as

a way to create a large logical

disk out of two or morephysical ones.

RAID Levels

RAID Levels

Raid 1:

It creates an exact copy or

mirror of set of data on two

disks. This is useful when read

performance is more important

than data storage capacity.

Write through-put is always

slower because every drive

must be updated on each

entry.

Raid 2:

It Stripes data at bit level and uses hamming code for error

correction. All disks participate in the execution of every I/O.

The spindles of individual disks are synchronized so that each

disk head is in the same position on each disk at any time.

RAID 2 is seldom deployed because costs to implement are usually prohibitive and gives poor performance with some disk I/O operations.

RAID Levels

Raid 3:

It stripes data at byte-level with

dedicated parity bit. All disks

are synchronized such that

each bit is on different drive.

Raid 3 is not commonly used.

All disks can accessed in

Parallel.

RAID Levels

Raid 4:

It stripes data at block-level with dedicated parity bit.

It is very rarely used in practice. Net App is the enterprise that

previously used this Raid.

This approach allows multiple writes to be done but that makes

performance slower.

RAID Levels

Raid 5:

It stripes data at block-level with distributed parity. Parity

information is distributed among the drives. Upon failure of a

single drive , subsequent reads can be calculated so no data

is lost. It requires at least three disks.

RAID Levels

Raid 6:

It stripes data at block-level with double distributed parity.

Double parity provides fault tolerance upto two drives.

Performance varies depending on how it is implemented.

RAID Levels

Feature R-0 R-1 R-2 R-3 R-4 R-5 R-6

Minimum

drives

2 2 3 3 3 3 4

Fault

Tolerance

0 N-1 1 1 1 1 2

Read

Performance

High High High High High High High

Write

Performance

High Medium Medium Low Low Low Low

Capacity

Utilization

100% 50% 50% 67-

94%

50-

88%

50-

88%

50-

88%

Best Raid Level???

Thank You!