Write-Through Cache - Dell PowerVault MD3200i Owner's Manual

mirrored to the cache of the second controller before completion status is
issued to the host initiator. Write-Back Cache is enabled by default unless
cache mirroring is disabled.

Write-Through Cache

In write-through cache, data is written to the physical disk before completion
status is returned to the host operating system. Write-through cache is
considered more robust than write-back cache, since a power failure is less
likely to cause loss of data. The RAID controller automatically switches to
write-through if cache mirroring is disabled or if the battery is missing or has a
fault condition.
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Planning: RAID Controller Modules