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Table 8. Description of Figure 10
Number Description
1 Controller A cache backup battery unit
2 Controller B cache backup battery unit
3 Latch
4 Pull handle
The battery unit provides backup power to each controller's cache memory. Each
battery unit contains a sealed, rechargeable lithium ion battery. The battery unit can
maintain data in the cache for three days.
The battery chargers in the power supply and fan units perform a battery test when
the storage subsystem is started and on a regularly scheduled interval thereafter.
Data caching starts after the battery completes its battery tests.
The battery unit is hot-swappable. You can remove the battery unit for servicing and
then reinsert it while the DS4700 Express continues to perform I/O operations.
However, write I/O caching is disabled when the battery is in a failed state. Replace
the failed battery as soon as possible to minimize the time that the write IO caching
is disabled.
Information about the condition of the battery unit is conveyed by indicator LEDs on
the front of battery unit. (“Battery unit LEDs” on page 128 identifies the indicator
LEDs on the battery unit and explains the conditions that each LED indicates.)
ds470012
1
2
3
4
Figure 10. Battery unit
18 IBM System Storage DS4700 Express Storage Subsystem: Installation, User’s and Maintenance Guide