RAID
stands for “Redundant Array of Independent Disks”
On most situations you will be using one of the following four
levels of RAIDs.
§ RAID
0
§ RAID
1
§ RAID
5
§ RAID
10 (also known as RAID 1+0)
This article explains the main
difference between these raid levels along with an easy to understand diagram.
In all the diagrams mentioned below:
In all the diagrams mentioned below:
§ A,
B, C, D, E and F – represents blocks
§ p1,
p2, and p3 – represents parity
RAID 0
Following are the key
points to remember for RAID level 0.
§ Minimum
2 disks.
§ Excellent performance ( as blocks are striped
).
§ No redundancy ( no mirror, no parity ).
§ Don’t use this for any critical system.
Example
|
RAID Type:
|
RAID 0 (Stripe Set)
|
|
Drive Capacity (GB):
|
300
|
|
Number of drives in
RAID group required:
|
2
|
|
Total usable storage
capacity (GB)
|
600
|
|
Space efficiency
|
100%
|
|
Fault tolerance = 0
disk drives (none)
|
|
Another example
RAID 1
Following are the key Points
to remember for RAID level 1.
§ Minimum
2 disks.
§ Good performance ( no striping. no parity ).
§ Excellent redundancy ( as blocks are mirrored
).
Example
|
RAID Type:
|
RAID 1 (Mirror)
|
|
Drive Capacity (GB):
|
300
|
|
Number of drives in
RAID group required:
|
2
|
|
Total usable storage
capacity (GB)
|
300
|
|
Space efficiency
|
50%
|
|
Fault tolerance = 1
disk drive per RAID Group
|
|
Another example
RAID 5
Following are the key
points to remember for RAID level 5.
§ Minimum 3 disks.
§ Good performance ( as blocks are striped ).
§ Good redundancy ( distributed parity ).
§ Hot Spare option supported at the SAN level.
§ Best cost effective option providing both performance and
redundancy. Use this for DB that is heavily read oriented. Write operations
will be slow.
§ Because of parity, information all data are available in case one
of the disk fails. If extra (spare) disks are available, then reconstruction
will begin immediately.
§ In short RAID 5 can survive one disk failure, but not two or
more.
Example
|
RAID Type:
|
RAID 5 (Stripe set with parity)
|
|
Drive Capacity (GB):
|
300
|
|
Number of drives in
RAID group required:
|
3
|
|
Total usable storage
capacity (GB)
|
600
|
|
Space efficiency
|
66.67%
|
|
Fault tolerance = 1
disk drive per RAID Group
|
|
RAID 10
Following are the key
points to remember for RAID level 10.
§ Minimum 4 disks.
§ This is also called as “stripe of mirrors”
§ Excellent reducdancy ( as blocks are mirroed).
§ Excellent performance (as blocks are striped)
§ If you can affored the cost, this is the BEST option for any
mission critical application (especially databases).
Example
|
RAID Type:
|
RAID 10 (Stripe set with parity)
|
|
Drive Capacity (GB):
|
300
|
|
Number of drives in
RAID group required:
|
4
|
|
Total usable storage
capacity (GB)
|
600
|
|
Space efficiency
|
50 %
|
|
Fault tolerance = 1 (min)
to 2 (max) disk drives per RAID Group
|
|
