HP StorageWorks 1500cs Modular Smart Array - Manual (Page 67)

Drive arrays and fault-tolerance methods 67
Item RAID 0 RAID 1+0 RAID 5 RAID 6 (ADG)
Tolerates simultaneous failure of
more than one physical drive No Only if no two
failed drives are
in the same
mirrored pair No Yes
Read performance High High High High
Write performance High Medium Low Low
Relative cost Low High Medium Medium
*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
NOTE: Not all controllers support RAID 6 (ADG).
Most important criterion Also important Suggested RAID level
Fault tolerance Cost effectiveness
I/O performance
RAID 6 (ADG)
RAID 1+0
Cost effectiveness Fault tolerance
I/O performance
RAID 6 (ADG)
RAID 5 (RAID 0 if fault tolerance is not required)
I/O performance Cost effectiveness
Fault tolerance
RAID 5 (RAID 0 if fault tolerance is not required)
RAID 1+0
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.
• Controller duplexing uses two identical controllers with independent, identical sets of drives
containing identical data. In the unlikely event of a controller failure, the remaining controller and
drives will service all requests.
Neither of these alternative fault-tolerance methods supports online spares or automatic data recovery, nor
do they support auto-reliability monitoring or interim data recovery.
If you decide to use one of these alternative methods, configure your arrays with RAID 0 for maximum
storage capacity and refer to your operating system documentation for further implementation details.