Raid Migration - HP 273914-B21 - Smart Array 6404/256 RAID Controller Technology Brief

Recommended stripe sizes
Table 4.
Type of server application
Mixed read/write
Mainly sequential read (such as audio/video
applications)
Mainly write (such as image manipulation
applications)
NOTE:
Different controllers may have different stripe sizes. Users should consult the controller
user guide for more details.

RAID migration

Using the ACU, administrators can also change the RAID level of the logical drive without downtime.
Administrators can perform RAID migration to increase raw data storage capacity, improve
performance by increasing the number of spindles in a logical drive, or change fault tolerance (RAID)
configurations. Table 5 summarizes RAID levels and the amount of space required for each type of
fault tolerance.
Table 5. Summary of RAID methods
Usable drive space*
Usable drives
Minimum number of
drives
Tolerant of single drive
failure?
Tolerant of multiple
simultaneous drive
failures?
Read performance
Write performance
Relative cost
* The values for usable drive space are calculated assuming a maximum of 14 physical drives of the same
capacity (or a maximum of 56 for RAID 6) with no online spares. HP recommends not exceeding these
maximum figures (excluding any allowable online spares) when configuring a drive array due to the increased
likelihood of logical drive failure with more disk drives.
RAID 0 RAID 1
(striping) (mirroring)
100% 50%
N N/2
1 2
No Yes
No No
High High
High Medium
Low High
Suggested stripe size change
Accept default value
Larger stripe sizes
Smaller stripes for RAID 5, RAID 6
Larger stripes for RAID 0, RAID 1, RAID 1+0
RAID 1+0 RAID 5
(striping and
mirroring)
50% 67% to 93%
N/2 N-1
4 3
Yes Yes
Yes, if failed No
drives not
mirrored to
each other
High High
Medium Low
High Medium
RAID 6
50% to 96%
N-2
4
Yes
Yes
High
Low
Medium
15