HP Surestore Disk Array 12h and FC60 - Manual (Page 67)

Capacity Management Features 67
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controller with 256 Mbytes of cache will use half of the memory to mirror the other
controller, leaving only 128 Mbytes for its own cache.
The write cache contents cannot be flushed when both controllers are removed from the
disk array simultaneously. In this case the write cache image is lost and data integrity on
the disk array is compromised. To avoid this problem, never remove both controllers from
the disk array simultaneously.
In the event of an unexpected disk array shutdown or loss of power, the BBU provides
power to cache memory to maintain the cache for 120 hours (5 days).
Dynamic Capacity Expansion
If slots are available in the disk enclosures, you can increase the capacity of the disk array
without disrupting operation. By simply adding new disks to the array and then creating a
new LUN the capacity can be expanded. See
"Adding Capacity to the Disk Array" on
page 254 for more information on adding disks and other ways of increasing disk array
capacity.