Which process minimizes the exposure to a loss of uncommitted cached data when there is a
power failure?

A.
Cache vaulting

B.
Cache mirroring

C.
Low watermarking

D.
Prefetching

Explanation:
Cache Data Protection
Cache is volatile memory, so a power failure or any kind of cache failure will cause loss of the data
that is not yet committed to the disk. This risk of losing uncommitted data held in cache can be
mitigated using cache mirroring and cache vaulting:
Cache mirroring: Each write to cache is held in two different memory locations on two independent
memory cards. If a cache failure occurs, the write data will still be safe in the mirrored location and
can be committed to the disk. Reads are staged from the disk to the cache; therefore, if a cache
failure occurs, the data can still be accessed from the disk. Because only writes are mirrored, this
method results in better utilization of the available cache. In cache mirroring approaches, the
problem of maintaining cache coherency is introduced. Cache coherency means that data in two
different cache locations must be identical at all times. It is the responsibility of the array operating
environment to ensure coherency.
Cache vaulting: The risk of data loss due to power failure can be addressed in various ways:
powering the memory with a battery until the AC power is restored or using battery power to write
the cache content to the disk. If an extended power failure occurs, using batteries is not a viable
option. This is because in intelligent storage systems, large amounts of data might need to be
committed to numerous disks, and batteries might not provide power for sufficient time to write
each piece of data to its intended disk. Therefore, storage vendors use a set of physical disks to
dump the contents of cache during power failure. This is called cache vaulting and the disks are
called vault drives. When power is restored, data from these disks is written back to write cache
and then written to the intended disks.
EMC E10-001 Student Resource Guide. Module 4: Intelligent Storage System