Dell PowerEdge 5/E, User Manual

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Glossary
Read-Ahead
A memory caching capability in some controllers that
allows them to read sequentially ahead of requested
data and store the additional data in cache memory,
anticipating that the additional data will be needed
soon. Read-ahead supplies sequential data faster, but
is not as effective when accessing random data.
Rebuild
The regeneration of all data to a replacement disk in a
redundant virtual disk (RAID level 1, 5, 10, or 50)
after a physical disk failure. A disk rebuild normally
occurs without interrupting normal operations on the
affected virtual disk, though some degradation of
performance of the disk subsystem can occur.
Rebuild Rate
The percentage of central processing unit (CPU)
resources devoted to rebuilding.
Reconstruct
The act of remaking a virtual disk after changing
RAID levels or adding a physical disk to an existing
virtual disk.
Redundancy
The provision of multiple interchangeable
components to perform a single function to cope with
failures and errors. Common forms of hardware
redundancy are disk mirroring, implementations of
parity disks, or distributed parity.
Redundant Virtual Disk
A redundant virtual disk is one which has redundant
data on physical disks in the disk group that can be
used to rebuild a failed physical disk. A virtual disk
can use disk striping across the physical disks, disk
mirroring or parity to provide redundancy. This offers
protection in case of a physical disk failure.
Replacement Disk
A physical disk replacing a failed member disk in a
virtual disk.
Replacement Unit
A component or collection of components in a system
or subsystem that is always replaced as a unit when
any part of the collection fails. Typical replacement
units in a disk subsystem include disks, controller
logic boards, power supplies and cables.
RPM
Acronym for Red Hat Package Manager. RPM is a
software manager used to install, remove, query, and
verify the software on your system. RPMs are used in
the driver update procedures for Red Hat Enterprise
Linux and SUSE LINUX Enterprise Server (SLES).
S
SAS
Acronym for Serial Attached SCSI. SAS is a serial,
point-to-point, enterprise-level device interface that
leverages the proven Small Computer System
Interface (SCSI) protocol set. The SAS interface
provides improved performance, simplified cabling,
smaller connectors, lower pin count, and lower power
requirements when compared to parallel SCSI. PERC
5 controllers leverage a common electrical and
physical connection interface that is compatible with
Serial ATA technology.
SATA
Acronym for Serial Advanced Technology
Attachment. A physical storage interface standard, is
a serial link that provides point-to-point connections
between devices. The thinner serial cables allow for
better airflow within the system and permit smaller
chassis designs.
Dell_PERC5_UG.book Page 106 Tuesday, February 13, 2007 6:02 PM