EMC Symmetrix DMX-3, Product Manual, Page: 213 / 326

Sparing in Symmetrix systems 213
Data Integrity, Availability, and Protection
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A failing drive cannot be spared with a different speed, block size,
or capacity; even 10K and 15K are not compatible (permanent
sparing).
◆
The spare cannot be on the same port, disk director, or loop as any
of the mirrors or RAID members of the failed disk (permanent
sparing).
◆
For permanent sparing purposes, Enginuity attempts to avoid
invoking a dynamic spare on the same disk director as the failing
drive. Enginuity uses this rule so that an uninvoked dynamic
spare on the same disk director can be used for the permanent
spare swap.
Sparing benefits In summary, sparing offers the following benefits:
◆
Significantly decreases the amount of time required to rebuild
and copyback the data from the failed drive.
◆
Permanent sparing has a lower total affected time than dynamic
sparing.
◆
Increases protection of all volumes from loss of data.
◆
Automatically activates the spare volume without interruption
prior to loss of access to a potentially failing volume.
◆
Ensures that the spare copy is identical to the original copy.
◆
Increases data availability of all volumes in use without loss of
any data capacity.
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Is transparent to the host and requires no user intervention.
◆
Resynchronizes a new disk drive with the dynamic spare after
repair of the defective device is complete.
Permanent sparing
Symmetrix systems have a permanent sparing functionality that
reserves volumes as standby spares. These volumes are not
user-addressable. Enginuity determines when a physical volume is
about to fail and initiates a rebuild and copyback (in parallel) of the
contents of the disk drive on which that volume resides to an
available spare without any interruption in processing. A failing
drive cannot be spared with a different speed, block size, or capacity;
even 10 K and 15 K drive speeds are not compatible. Drives that
contain vault volumes are candidates for permanent sparing if there
is an available spare on the same primary loop.