Raid and its levels

1. RAID and Its Levels
Presented By:
Hassan Mehmood
2419
Semester:
7th(BS.IT)

2. 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

3. 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

4. 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.

5. 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

6. Raid 0:
It splits data evenly across two
Or more disks. RAID 0 is normally
used to increase performance,
although it can also be used as
a way to create a large logical
disk out of two or more
physical ones.
RAID Levels

7. 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.

8.  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

9.  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

10.  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

11.  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

12.  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

13. 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???

14. Thank You!