Sparing in Symmetrix systems
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Data Integrity, Availability, and Protection
Sparing in Symmetrix systems
Symmetrix DMX-3 systems support both permanent sparing and
dynamic (temporary) sparing functionality. Sparing increases data
availability with minimum impact on performance. It is used in
combination with all protection types, for example, mirroring,
RAID 5, RAID 6, or SRDF.
Note: When a failing drive occurs, permanent sparing is automatically
invoked by the Symmetrix system. If there is not a spare located in a good
location (No spare suitable for a permanent swap, or unprotected volumes on
the bad drive that will need to be copied to a dynamic spare before the swap
is performed.), then dynamic sparing is automatically invoked.
Symmetrix maintains a pool of spares in various locations that can be
used to support both permanent and dynamic sparing.
Sparing
configuration rules
and guidelines
for the DMX-3 it is recommended to configure spare drives
proportional to the amount of each type of drive configured in the
Symmetrix. Calculate the number and types of spares for DMX-3
systems as follows:
â—† Two spare drives for each type of drive in the system
â—† One additional spare drive for every 100 drives or portion thereof
for each type of drive in the system
Special DMX-3
sparing
considerations
Additional spare drives may be required in certain DMX-3
configurations. In the case of RAID 5 (7+1) or RAID 6 (14+2) on both
the two-director pair DMX-3 950 and the DMX-3, one spare drive
needs to be configured on every loop in order to fully implement
permanent sparing. Configuring fewer spares would mean that only
those drives with a spare on the same loop could be permanently
spared.
Furthermore, since only one spare is available for each drive, then the
spare would need to be replaced before permanent sparing again
fully protects the entire system. In these special circumstances the
option to allow a number of drives to fail and maintain the ability to
permanently spare all drives is not available. Configuring two or
more spares per loop will alleviate this issue.
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