Cache memory
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 74 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 DCS3700 storage system 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 74 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
when the Battery fault LEDs indicate that only one battery unit has failed. Each controller has a green
Battery charging LED that indicates the status of the battery unit.
v The LED is on when the battery is fully charged
v The LED flashes when the battery is charging or performing a self-test
v The LED is off when the battery or the battery charger has failed or is missing
Cache battery learn cycle
The battery performs a learn cycle the first time the storage subsystem is turned on, and again every
eight weeks thereafter, to assess the charge capacity of the battery. If the battery fails the learn cycle or
takes too much time to reach full charge, the Battery charging LED turns off, the Battery fault LED turns
on and the Storage Manager identifies the battery as failed.
The learn cycle takes up to three hours. During this time, the cache will be active if the battery is in
optimal condition. If the learn cycle is interrupted, the current learn cycle will be terminated and the
battery will perform a new learn cycle at the next scheduled interval (eight weeks from the current learn
cycle). A learn cycle interruption is caused by removing the battery from the controller chassis, resetting
the power to the storage subsystem, or if an storage enclosure or battery overheats.
82 IBM System Storage DCS3700: Installation, User, and Maintenance Guide
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