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About Your System 23
Battery Backup Unit
Each RAID controller contains a three-cell lithium-ion battery backup unit
(BBU) that powers the controller’s cache memory and preserves the cache
contents in the event of a power outage of up to 72 hours. The RAID
controller firmware performs a test of the BBU at startup and will illuminate
the battery fault LED if the battery is not operating within specified ranges,
or if the battery is missing. The battery begins recharging automatically if the
test determines that it is necessary. For a description of the battery fault LED,
see Table 1-4. For information on removing and installing the BBU, see
"Removing and Installing a RAID Controller Module Backup Battery Unit"
on page 62.
NOTE: For virtual disks, the RAID controller firmware changes the data cache
setting based on the state of the battery. If the battery is missing or does not have
sufficient charge, the controller flushes the cache and sets the write cache
attribute to Write Through for all virtual disks. When the battery is replaced, Write
Back is reenabled.
The RAID controller module logs the age of the battery and issues a
replacement reminder message approximately six weeks before expiration.
After replacing the battery, you must use MD Storage Manager to reset the
battery age.
RAID Enclosure Thermal Shutdown
Enclosure management provides a feature that automatically shuts down the
enclosure when the temperature within the storage enclosure exceeds a safe
threshold. Thermal shutdown protects the data on the physical disks from
corruption in the event of cooling system failure. Because the battery backup
unit
protects against cache data loss for up to 72 hours,
all data in the cache is
saved. It is not necessary to shut down any expansion enclosures attached to
the storage enclosure.
Temperature threshold values are used to determine the temperature at
which shutdown occurs. These thresholds are default settings and cannot be
changed. If the temperature sensors on the backplane detect a temperature
exceeding the Nominal Failure Threshold, a critical event is set. If the
Maximum Failure Threshold is reached, shutdown of the enclosure power
supplies occurs within 3 minutes. A third threshold, the Shutdown Threshold,
shuts down the enclosure power supplies within 5 seconds after it is reached.