HP ProLiant ML310e Configuring Arrays on HP Smart Array Controllers Reference - Page 103

Selecting a RAID method, Alternative fault-tolerance methods, RAID 0, Most important criterion

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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 RAID 0 Striping (no fault tolerance) n 100% 1 No No High High Low RAID 1+0 Mirroring n/2 50% 2 Yes Only if no two failed drives are in the same mirrored pair High Medium High RAID 5 Distributed Data Guarding n-1 67% to 93% 3 Yes No High Low Medium RAID 6 (ADG) Advanced Data Guarding n-2 50% to 96% 4 Yes Yes High Low 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 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 Also important Suggested RAID level Fault tolerance Cost effectiveness I/O performance Cost effectiveness I/O performance Fault tolerance I/O performance Cost effectiveness Fault tolerance RAID 6 RAID 1+0, RAID 50, RAID 60 RAID 6 RAID 5 (RAID 0 if fault tolerance is not required) RAID 5 (RAID 0 if fault tolerance is not required) RAID 1+0, RAID 50, RAID 60 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. Drive arrays and fault-tolerance methods 103

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Drive arrays and fault-tolerance methods
103
Item
RAID 0
RAID 1+0
RAID 5
RAID 6
(ADG)
Alternative name
Striping (no
fault
tolerance)
Mirroring
Distributed
Data
Guarding
Advanced
Data
Guarding
Formula for number of drives
usable for data (
n
= total number
of drives in array)
n
n
/2
n
-1
n
-2
Fraction of drive space usable*
100%
50%
67% to 93%
50% to 96%
Minimum number of physical
drives
1
2
3
4
Tolerates failure of one physical
drive
No
Yes
Yes
Yes
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
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
(
).
Most important criterion
Also important
Suggested RAID level
Fault tolerance
Cost effectiveness
I/O performance
RAID 6
RAID 1+0, RAID 50, RAID 60
Cost effectiveness
Fault tolerance
I/O performance
RAID 6
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, RAID 50, RAID 60
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.