Specifications

GL–18 Glossary
RAID level 3/5 A DIGITAL-developed RAID storageset that stripes data and parity across three or
more members in a disk array. A RAIDset combines the best characteristics of
RAID level 3 and RAID level 5. A RAIDset is the best choice for most applications
with small to medium I/O requests, unless the application is write intensive. A
RAIDset is sometimes called parity RAID. Raid level 3/5 storagesets are sometimes
referred to as RAIDsets.
RAIDset
See RAID level 3/5.
RAM Random access memory.
read ahead caching A caching technique for improving performance of synchronous sequential reads
by prefetching data from disk.
read caching A cache management method used to decrease the subsystem’s response time to
a read request by allowing the controller to satisfy the request from the cache
memory rather than from the disk drives.
reconstruction The process of regenerating the contents of a failed member’s data. The
reconstruct process writes the data to a spareset disk and then incorporates the
spareset disk into the mirrorset, striped mirrorset, or RAIDset from which the failed
member came.
See also regeneration.
reduced Indicates that a mirrorset or RAIDset is missing one member because the member
has failed or has been physically removed.
redundancy The provision of multiple interchangeable components to perform a single function
in order to cope with failures and errors. A RAIDset is considered to be redundant
when user data is recorded directly to one member and all of the other members
include associated parity information.
regeneration (1) The process of calculating missing data from redundant data. (2) The process
of recreating a portion of the data from a failing or failed drive using the data and
parity information from the other members within the storageset. The regeneration
of an entire RAIDset member is called reconstruction.
See also reconstruction.