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Functional and Operational Characteristics 3-27
Hitachi Universal Storage Platform V/VM User and Reference Guide
Battery Backup Operations
Figure 3-6 illustrates the two types of backup operations: backup mode and
destage mode.
Backup Mode (USP V and VM)
When backup mode is chosen and a power failure occurs, storage system
operations will continue normally for 200 milliseconds. If the power failure
exceeds 200 ms, the storage system uses power from the batteries to back
up the cache memory and shared memory for 36 hours or 48 hours,
depending on the amount of cache memory.
Destage Mode (USP V only)
When destage mode is chosen and a power failure occurs, storage system
operations will continue normally for 1 minute. If the power failure exceeds
1 minute, the storage system uses power from the batteries to destage the
data from cache memory onto the disk drives and back up the cache
memory and shared memory for 18 hours or 24 hours, depending on the
amount of cache memory.
Destage mode requires the 56V battery option (DKC-F610I-ABX).
Note: Destage mode is not supported in the following cases:
– When external storage is connected
– When Cache Residency Manager BIND mode is applied.
Battery Charge
If the battery is not fully charged when a power failure occurs, the backup
processes are affected as follows:
– Backup mode: The backup time becomes short (less than 36/48 hours).
– Destage mode: The destage process may not be possible until the
battery charging is complete, and the backup time may also become
short (less than 18/24 hours).