using parity data onto a spare disk, preventing
data loss.
parity scrub
A RAID data verification scheme which checks
all parity data in a RAID and makes sure that it is
correct. In Nexsan storage systems, the parity
scrub utility also performs a surface scan.
pod
See “active drawer”.
pool spare
See “spare disk”.
power supply unit
A module that regulates electrical power to the
components of Nexsan storage units.
provisioning
Directly accessing and configuring RAIDs and
volumes on a Nexsan storage system without
use of the graphical user interface. See also
“VDS Storage Provisioning”.
PSU
See “power supply unit”.
R
RAID
Redundant Array of Independent Disks. A
system using multiple hard drives organized into
a single logical unit for the sharing or replication
of data in order to increase data integrity, fault-
tolerance, and throughput. Also referred to as a
RAID set. RAIDs are organized into
RAID levels, which describe their architecture
and configuration.
RAID controller
A hardware device, software program, or
combination of the two which manages the
physical disk drives in an array and presents
them as a single logical unit to attached devices.
The RAID Controllers in Nexsan storage units
are hardware modules. Nexsan RAID
Controllers also provide connections for system
administration and configuration.
RAID level
A numeric indicator of the architecture used by a
RAID. RAIDs can be built using any combination
of striping, mirroring, and parity. The levels are
numbered from 0 through 6. Some RAID levels
can also be combined, and these configurations
are usually referred to with a two-digit number.
For example, RAID 10 = RAID 1 + RAID 0.
RAID set
See “RAID”.
read-only memory (ROM)
A memory chip that stores values but cannot be
changed by normal program instructions. Values
in read-only memory are nonvolatile; they are
retained even when the unit is powered down.
reboot
To restart a computer or computerized electronic
device. See also system reboot.
redundant
The duplication of critical components or
functions of a system with the intention of
increasing the reliability of the system. RAID
sets are redundant when one or more spare disks
are available to it.
replica
A duplicate of a volume on a Nexsan storage
system copied onto another Nexsan storage
system. At the time of replication, replicas
contain all of the data on the original volume.
Replicas can be promoted to full volumes, after
which replication between the two volumes is no
longer possible.
replication
A function of Nexsan storage systems that
allows the user to make replicas of a volume
onto another Nexsan storage system to protect
data in the event of a disaster or as part of a
backup and restore architecture.
rolling restart
On Nexsan storage systems, a method of
rebooting both RAID controllers in a unit so that
host I/O is not interrupted. Rolling restart is only
available if the unit’s system mode is set to 2-
Glossary
Nexsan High-Density Storage
User Guide
262