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EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
The Symmetrix system notifies the EMC Customer Support Center of
this event with an Environmental-Data Present error. The permanent
sparing option increases data availability with minimum impact on
performance. Permanent sparing has the added benefit of allowing
an EMC Customer Engineer operating on site or from the EMC
Customer Support Center to force the Symmetrix system to
rebuild/copyback the contents of a device to a permanent spare. This
forced copy allows the EMC Customer Engineer to test or service a
disk drive nondisruptively while access to data continues.
Permanent sparing
process
The permanent sparing process follows these steps: (Figure 48 on
page 215):
1. Enginuity determines when a physical volume is about to fail.
The Symmetrix system makes its copying decision based on error
statistics maintained by its directors, the intelligent disk
microprocessor self-testing information, and its active error
checking system.
2. If the Symmetrix sparing algorithms determine that the number
of errors occurring on a volume is excessive and that a hard
failure is probable, the sparing process starts one or two of the
following processes:
a. Looks for an available spare in its pool of spares, dynamically
invokes it, and initiates the rebuild.
b. Looks for and identifies a spare drive of the same capacity and
speed in a good location to permanently replace the failing
drive.
The process identifies a good location using the following
rules:
– Not on the same disk director as any other member of the
RAID group
– Not on the same loop or drive enclosure as any other
member of the RAID group
– Not on the same power branch as any other member of the
RAID group
Note: If a suitable permanent spare cannot be identified, dynamic
sparing will continue.“Dynamic sparing” on page 216 provides more
information on the dynamic sparing process.
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