Data integrity and availability are critical in today’s business environment. Smart Array controllers
are used to maximize the performance of the storage system and to preserve data. The process of
transferring data to and from disk storage includes storing the data temporarily in cache memory
located on the RAID array controller that is managing the data transfer.

Allowing the controller to cache write data in its local memory improves write speed, however, it
exposes you to a risk of having the operating system think that data has already been written to
the disk. In this case, having power fail before the controller completes the writes can result in
a data loss.

The battery backup allows the data in the cache to survive until the machine is powered on again,
mitigating the risk. Because of this, it is important to have a working RAID battery at all times. If the
PSU suddenly stops working, regardless of a UPS, your system is down and you may have had
uncommitted data in your RAID cache.

Working RAID battery ensures that the data is correctly written when the power is restored. The
same is true if you had a system board failure. Even if the RAID controller has to be replaced, if there
is a working RAID battery-backed cache, it can be moved to a new card without data loss.

Battery backing of cache is only as good as the remaining capacity of the batteries. A battery
maintenance program should include battery replacement within three years unless other specific
actions are taken.