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DELL PERC H700 and H800 Technical Guide 18
being a ready hot spare. This allows hot spares to remain in specific enclosure slots. While the
controller is reverting the hot spare, the virtual disk remains optimal. The controller automatically
reverts a hot spare only if the failed drive is replaced with a new drive in the same slot. If the new
drive is not placed in the same slot, a manual Replace Member operation can be used to revert a
previously commissioned hot spare.
4.5.6 Enclosure Affinity
Enclosure affinity is used to set the preference for a hot spare to be used to rebuild a physical disk
that resides in the same physical enclosure. This does not preclude the hot spare from being
provisioned to a second enclosure if there are no other hot spares present. For example, if there are
two enclosures and each enclosure has a hot spare with affinity set, then upon a drive failure the hot
spare will be provisioned from the same enclosure as the failed drive.
Hot-spare enclosure affinity can be configured only if you are using an external storage enclosure.
4.5.7 Battery Back-up of Controller Cache
4.5.7.1 Battery Management
The transportable battery backup unit (TBBU) is a cache memory module with an integrated battery
pack that enables you to transport the cache module with the battery in a new controller. The TBBU
protects the integrity of the cached data on the PERC H800 adapter by providing backup power
during a power outage. The battery backup unit (BBU) is a battery pack that protects the integrity of
the cached data on the PERC H700 cards by providing backup power during a power outage. The
battery provides up to 24 hours of backup power for the cache memory.
4.5.7.2 Battery Learn Cycle
Learn cycle is a battery calibration operation performed by the controller periodically to determine
the condition of the battery. This operation cannot be disabled.
The time frame for completion of a learn cycle is a function of the battery charge capacity and the
discharge/charge currents used. For PERC H700 or H800 cards, the expected time frame for
completion of a learn cycle is approximately seven hours and consists of the following parts:
• Learn cycle discharge cycle: approximately three hours
• Learn cycle charge cycle: approximately four hours
During the discharge phase of a learn cycle, the PERC H700 or H800 battery charger is disabled and
remains disabled until the battery is discharged. After the battery is discharged, the charger is re-
enabled.
4.6 Physical Disk Hot Swapping
Hot swapping is the manual replacement of a unit in a disk subsystem while the subsystem is
performing its normal functions. The following requirements must be met before hot swapping a
physical disk:
• The system backplane or enclosure must support hot swapping.
• The replacement drive must be of the same protocol and drive technology. For example, only
a SAS HDD can replace a SAS HDD; only a SATA SSD can replace a SATA SSD.
• The replacement drive must be of equal or greater capacity than the one it is replacing.