HP 4000.6000.8000 Enterprise Virtual Arrays - Manual (Page 172)

read ahead
caching A cache management method used to decrease the subsystem response time to a read request
by allowing the controller to satisfy the request from the cache memory rather than from the disk
drives.
read caching A cache method used to decrease subsystem response times to a read request by allowing the
controller to satisfy the request from the cache memory rather than from the disk drives. Reading
data from cache memory is faster than reading data from a disk. The read cache is specified as
either On or Off for each virtual disk. The default state is on.
reconstruction The process of regenerating the contents of a failed member data. The reconstruction process
writes the data to a spare set disk and incorporates the spare set disk into the mirrorset, striped
mirrorset or RAID set from which the failed member came.
redundancy Element Redundancy—The degree to which logical or physical elements are protected by
having another element that can take over in case of failure. For example, each loop of a 1.
device-side loop pair normally works independently but can take over for the other in case
of failure.
2. Data Redundancy—The level to which user data is protected. Redundancy is directly
proportional to cost in terms of storage usage; the greater the level of data protection, the
more storage space is required.
redundant power
configuration A capability of the Enterprise storage system racks and enclosures to allow continuous system
operation by preventing single points of power failure.
•
For a rack, two AC power sources and two power conditioning units distribute primary and
redundant AC power to enclosure power supplies.
•
For a controller or drive enclosure, two power supplies ensure that the DC power is available
even when there is a failure of one supply, one AC source, or one power conditioning unit.
Implementing the redundant power configuration provides protection against the loss or
corruption of data.
reporting group An Enterprise Storage System controller pair and the associated disk drive enclosures. The
Enterprise Storage System controller assigns a unique decimal reporting group number to each
EMU on its loops. Each EMU collects disk drive environmental information from its own
sub-enclosure and broadcasts the data over the enclosure address bus to all members of the
reporting group. Information from enclosures in other reporting groups is ignored.
room temperature See ambient temperature.
S
SCSI-3 The ANSI standard that defines the operation and function of Fibre Channel systems.
SCSI-3 Enclosure
Services See SES.
selective
presentation The process whereby a controller presents a virtual disk only to the host computer which is
authorized access.
serial transmission A method of transmission in which each bit of information is sent sequentially on a single channel
rather than simultaneously as in parallel transmission.
SES SCSI-3 Enclosures Services. Those services that establish the mechanical environment, electrical
environment, and external indicators and controls for the proper operation and maintenance of
devices within an enclosure.
snapclone A virtual disk that can be manipulated while the data is being copied. Only an Active member
of a virtual disk family can be snapcloned.
The Snapclone, like a snapshot, reflects the contents of the source virtual disk at a particular point
in time. Unlike the snapshot, the Snapclone is an actual clone of the source virtual disk and
immediately becomes an independent Active member of its own virtual disk family.
snapshot A temporary virtual disk (Vdisk) that reflects the contents of another virtual disk at a particular
point in time. A snapshot operation is only done on an active virtual disk. Up to seven snapshots
of an active virtual disk can exist at any point. The active disk and its snapshot constitute a virtual
family.
See also active virtual disk, and virtual disk family.
172 Glossary