Dell PowerEdge 5/E, User Manual

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Glossary
101
Disk Subsystem
A collection of disks and the hardware that controls
them and connects them to one or more controllers.
The hardware can include an intelligent controller, or
the disks can attach directly to a system I/O bus
controller.
Distributed Parity
Parity involves an extra bit added to a byte or word to
reveal errors in storage (in RAM or disk) or transmission.
Parity is used to generate a set of redundancy data
from two or more parent data sets. The redundancy
data can be used to rebuild one of the parent data
sets. In distributed parity, the parity data are
distributed among all the physical disks in the system.
If a single physical disk fails, it can be rebuilt from the
parity of the applicable data on the remaining
physical disks.
DKMS
Acronym for Dynamic Kernel Module Support.
Designed by Dell™, DKMS creates a framework in
which kernel-dependent module source can reside so
that it is easy to rebuild modules as you upgrade
kernels. DKMS is used in the upgrade process for
drivers for Red Hat
®
Linux and SUSE
®
Linux
Enterprise Server.
DUD
Acronym for driver update diskette. A DUD is an
image of a diskette stored as a regular file. To use it,
you have to create a real diskette from this file. The
steps used to create the diskette depend on how the
image is supplied.
E
ECC Errors
Acronym for error correcting code. ECC errors occur
in the memory and can corrupt cached data so that it
must be discarded. Single-bit ECC errors can be
handled by the firmware and do not disrupt normal
operation. A notification will be sent if the number of
single-bit errors exceeds a threshold value. ECC
double-bit errors are more serious, as they result in
corrupted data and data loss.
Enclosure
A structure, such as a system, which contains physical
disks that are grouped together to create virtual disks.
Enclosure Management
Intelligent monitoring of the disk subsystem by
software and/or hardware. The disk subsystem can be
part of the host system or can reside in an external
disk enclosure. Enclosure management helps you stay
informed of events in the disk subsystem, such as a
physical disk or power supply failure. Enclosure
management increases the fault tolerance of the disk
subsystem.
Exclusive-OR
A Boolean operation used to create a parity bit that
can be used to restore data affected by a damaged file
or failed physical disk. The management utility
compares data from two physical disks and creates a
parity bit that is stored on a third physical disk. This
operation is used for RAID levels that use parity bits,
such as RAID 5, which used distributed parity. Also
known as X-OR.
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