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In addition to the above, there are still other considerations. For
example, a spare drive carries no data stripes and will not
contribute to disk-level performance. Please refer to the
documentation by the hard drive manufacturers for performance
data.
˙
When cabling, follow all the SAS interface specifications. Pay
attention to signal quality and avoid electronic noise from
adjacent interfaces, e.g., do not lay power cords on data cables.
˙
RAID arrays adopt a "least-common-denominator" approach.
The maximum capacity of each drive used in the array is the
maximum capacity of the smallest drive. Therefore, it is
suggested that you use the drives with the same capacity not
only in the same logical drive but also in the whole configuration.
Mixing drives of different sizes and speeds can cause some
operation problems. Mixing drives in RAID enclosures and
JBODs is supported, e.g., 150GB SAS drives in your RAID
enclosure and 750GB SATA drives in JBODs. However, you
should not include SAS and SATA drives in a logical drive.
˙
A spare drive should have a minimum capacity that is equivalent
to the largest drive that it is expected to replace. If the capacity
of the spare is less than the capacity of the drive it is expected to
replace, the controller will not proceed with the failed drive
rebuild.
When the configuration consists of multiple enclosures, it is
suggested that you use the firmware function "Enclosure
Spare" instead of the "Global Spare," to avoid a spare drive
participating in the rebuild of drives in another enclosure.
Chapter 3: System Connections
3-3
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