Specifications

GL–16 Compaq StorageWorks HSG80 Array Controller ACS Version 8.5 Maintenance and Service Guide
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.