Selecting A Raid Method; Alternative Fault-Tolerance Methods - HP ProLiant DL360p Reference Manual

Item
Alternative name
Formula for number of drives usable
for data (n = total number of drives in
array)
Percentage of drive space usable*
Minimum number of physical drives
Tolerates failure of one physical drive No
Tolerates simultaneous failure of
more than one physical drive
Read performance
Write performance
Relative cost
*Values for the percentage 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

Not all controllers support all RAID levels. 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.
•
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.
RAID 0 RAID 1+0
Striping (no Mirroring
fault
tolerance)
n n/2
100% 50%
1 2
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 10 (ADM), 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 10 (ADM), 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% 33%
3 4
Yes Yes
No Yes
High High
Low Low
Medium Medium
Drive arrays and fault-tolerance methods 117
RAID 1(0)
(ADM)
Advanced
Data
Mirroring
n/3
3
Yes
Only if no
three drives
are in the
same mirror
group
High
Medium
Very high