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 90 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 90 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
102 IBM System Storage DS3500 and EXP3500 Storage Subsystem: Installation, User's, and Maintenance Guide
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