IBM TotalStorage FAStT200, Installation And User Manual

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IBM FAStT200 and FAStT200 HA Storage Servers Installation and User’s Guide
Cache memory and RAID controller battery
Each RAID controller contains 4 KB of cache data. It also contains a rechargeable
battery that maintains data in the cache in the event of a power failure. The following
sections describe these features and their associated LEDs.
Cache memory
Cache memory is memory on the RAID controller that is used for intermediate storage
of read and write data. Using cache memory can increase system performance. The
data for a read operation from the host might be in the cache memory from a previous
operation (thus eliminating the need to access the drive itself), and a write operation is
completed when it is written to the cache, rather than to the drives.
See the storage-management software documentation for information on setting
cache memory options.
The RAID controller has a Cache active LED that displays the current status of the
cache. The LED is on if there is data in the cache, and it is off if there is no data in the
cache.
If caching is enabled and the Cache active LED never comes on during I/O activity, it
indicates that the cache memory has failed or the battery has failed (the green Battery
LED will be off).
Note: Always use the storage-management software to check your cache memory
settings before assuming a hardware failure.
The following illustration shows the location of the Cache active LED on the front of
the RAID controller.
Cache active LED