RAID and Subsystem Architectures
• Cache is volatile memory – lost during power-outage
• Data in cache is not immediately written to disk
• To protect data in cache, the cache memory has internal battery
protection – preserves unwritten data for days until disks are re-
powered and data can finally be written to disk.
• High end subsystems also use mirrored cache for high-availability
• Use of Error Checking (ECC) codes can detect & correct memory
Remember that data sitting in the cache memory may not have yet been
written to the physical disk.
Thus, if we get a power failure there is a risk of loss of the changes to the data
that have not yet been written to disk.
High end storage arrays use a number of techniques to protect data held in
Battery Protection of Cache memory
Mirroring of cached data into two different physical sets of cache
Error checking on cache memory, can detect & correct memory errors