Cache Memory And Cache Battery; Cache Memory; Controller Cache Battery - IBM DS3500 Installation, User's, And Maintenance Manual

11. Replace the bezel on the storage enclosure, if applicable.

Cache memory and cache battery

Each storage controller in the DS3500 storage subsystem contains 1 GB or 2 GB of cache memory to store
read and write operations. In a dual controller configuration, both controllers in the DS3500 must have
the same amount of cache memory. The battery unit contains enough charge to back up the cached data
in each controller to a flash drive in the event of a DS3500 power failure.

Cache memory

Cache memory is memory on the storage controller that is used for intermediate storage of read and write
data on the DS3500 controllers. 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.
The controller has a cache active LED that indicates the current status of the cache. The LED is lit when
there is data in the cache, and it is off when there is no data in the cache.
If caching is enabled and the cache active LED is not lit during I/O activity, it indicates one of the
following conditions:
v The cache memory from either controller A or controller B has failed
v The cache sizes in controller A and controller B are not the same
v The battery has failed
Note: Always use the Storage Manager client to check the cache memory settings before you assume that
a hardware failure has occurred.
See "Controller LEDs" on page 4-9 for the location of the cache active LED on a controller.

Controller cache battery

The backup battery unit provides power to back up the cache memory of each controller onto flash
drives in the event of a power failure. Each battery unit contains a sealed, rechargeable SMART lithium
ion battery.
CAUTION:
The battery is a lithium ion battery. To avoid possible explosion, do not burn. Exchange only with the
IBM-approved part. Recycle or discard the battery as instructed by local regulations. In the United
States, IBM has a process for the collection of this battery. For information, call 1-800-426-4333. Have
the IBM part number for the battery unit available when you call. (C007)
Replace the battery units in the DS3500 when they are identified as failing by the Storage Manager
Subsystem Management window, or when the battery fault LEDs light. See "Controller LEDs" on page
4-9 for the location of the battery fault LED.
Replace only the battery unit that is indicated as failed by the LEDs or in the Storage Manager Subsystem
Management window. In a dual controller configuration, you do not need to replace both battery units
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System Storage DS3500 and EXP3500: Installation, User's, and Maintenance Guide