506 IBM Midrange System Storage Hardware Guide
DS5000 arrays and RAID levels
An array is a set of drives that the system logically groups together to provide one or more
logical drives to an application host or cluster. When defining arrays, you often have to
compromise among capacity, performance, and redundancy. The DS5000 supports different
number of RAID types.
Table A-1 shows a support matrix for DS4000 and DS5000 systems to the RAID levels.
Table A-1 RAID support matrix for DS4000 and DS5000 storage subsystems
Generally, RAID 6 support is implemented in controller firmware version (CFW) 7.xx and
above, but it also requires the DS4000 and DS5000 XOR chip to be able to handle the
RAID 6 algorithm. DS4700 storage subsystem is the only DS4000 storage subsystems that is
able to support RAID 6 with CFW 7.xx and higher.
The DS4000 and DS5000 are also able to dynamically change the RAID type without
downtime. This feature is called Dynamic RAID Migration (DRM).
RAID levels
We go through the different RAID levels and explain why we choose a particular setting in a
particular situation; you can draw your own conclusions.
RAID 0: For performance, but generally not recommended
RAID 0 (Figure A-1 on page 507) is also known as data striping. It is well-suited for program
libraries requiring rapid loading of large tables, or more generally, applications requiring fast
access to read-only data or fast writing. RAID 0 is only designed to increase performance.
Since CFW 7.10, there is no limit for drives that belong to one RAID 0. CFW 6.xx limits the
number of drives to a maximum of 30 drives.
There is no redundancy, so any disk failures require reloading from backups. Select RAID 0
for applications that will benefit from the increased performance capabilities of this RAID
level, such as high performance computing (HPC) jobs. Never use this level for critical
applications that require high availability.
Subsystem RAID 0, 1, 10, 3, 5 RAID 6
DS4700 (CFW 6.xx) Yes No
DS4700 (CFW 7.xx) Yes Yes
DS5100/DS5300 Yes Yes
DS5020 Yes Yes
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