Selecting A Raid Method; Alternative Fault-Tolerance Methods - HP 166207-B21 - Smart Array 5302/32 RAID Controller Reference Manual

Item
Alternative name
Formula for number of drives
usable for data (n = total number
of drives in array)
Fraction of drive space usable*
Minimum number of physical
drives
Tolerates failure of one physical
drive
Tolerates simultaneous failure of
more than one physical drive
Read performance
Write performance
Relative cost
*Values for the fraction of drive space usable are calculated with these assumptions: (1) all physical drives in the
array have the same capacity; (2) online spares are not used; (3) no more than 14 physical drives are used per array
for RAID 5; and (4) no more than 56 drives are used with RAID 6 (ADG).

Selecting a RAID method

Some controllers do not support RAID 50, RAID 6, or RAID 60. To determine the RAID capabilities of your
controller, see the model-specific information for your controller on the HP website
(http://www.hp.com/products/smartarray).
Most important criterion
Fault tolerance
Cost effectiveness
I/O performance

Alternative fault-tolerance methods

Your operating system may also support software-based RAID or controller duplexing.
•
Software-based RAID resembles hardware-based RAID, except that the operating system works with
logical drives as if they were physical drives. To protect against data loss caused by physical drive
failure, each logical drive must be in a different array from the others.
RAID 0 RAID 1+0
Striping (no Mirroring
fault
tolerance)
n n/2
100% 50%
1 2
No Yes
No Only if no two
failed drives are
in the same
mirrored pair
High High
High Medium
Low High
Also important Suggested RAID level
Cost effectiveness RAID 6
I/O performance RAID 1+0, RAID 50, RAID 60
Fault tolerance RAID 6
I/O performance RAID 5 (RAID 0 if fault tolerance is not required)
Cost effectiveness RAID 5 (RAID 0 if fault tolerance is not required)
Fault tolerance RAID 1+0, RAID 50, RAID 60
RAID 5 RAID 6
(ADG)
Distributed Advanced
Data Data
Guarding Guarding
n-1 n-2
67% to 93% 50% to 96%
3 4
Yes Yes
No Yes
High High
Low Low
Medium Medium
Drive arrays and fault-tolerance methods 103