Figure 8 Intermixed RAID groups
.
Backup batteries
The XP24000/XP20000 disk arrays use batteries and two modes of backup operation to provide
backup power protection for cache memory, shared memory, the DKAs, CHAs, and disk drives. If
AC input power is lost, the disk array continues normal operation for 200 ms or 1 minute, depending
on whether the disk array is set for Backup Mode or De-stage Mode. See Figure 9.
If Backup Mode is selected and AC power is lost for more than 200 ms, the disk array enters the
Backup Mode, which maintains the contents of cache and shared memory for 36 to 48 hours,
depending on the amount of cache memory installed. This mode is the default and the only available
mode for the base battery configuration.
If De-stage Mode is selected and sufficient optional DKC and DKU backup batteries are installed, the
batteries maintain normal operation for 1 minute. After 1 minute without AC power, the disk array
executes the De-stage Mode, which saves the contents of cache and shared memory to disk, maintains
the contents of cache and shared memory for 16 to 24 hours, and powers down the system. Even if
power is restored shortly after one minute, the de-stage and power down processes continue until
they are completed.
XP24000/XP20000 Disk Array Owner's Guide 27
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