spare disk
A blank disk drive that is available to a RAID in
case any of the disks assigned to the RAID
should fail. If a RAID disk fails, the
RAID controller rebuilds the data from the failed
disk onto the spare disk, which then becomes
part of the RAID. In Nexsan storage systems,
there are two kinds of spare disk: “pool spares”,
which can be used by any RAID in the unit; and
“dedicated spares”, which are assigned to a
specific RAID.
SSD
Solid State Disk. A high-performance storage
device that contains no moving parts.
SSL
Secure Sockets Layer. A method of encrypting
communication between a web server and a web
browser. SSL requires the use of an SSL
certificate, which binds the encryption key to the
server. The SSL protocol secures input/output
(I/O) and serial port data. On Nexsan storage
systems, SSL is used to encrypt the connection
between the storage unit and any computer that
is accessing the unit’s graphical user interface.
storage area network
An architecture that provides for attachment of
remote computer storage devices to servers in
such a way that the devices appear as locally
attached to the operating system.
Storage Manager
One of six Nexsan Storage Tools. Storage
Manager provides a common management point
for all Nexsan storage systems, either in a
standalone window or directly integrated into
Windows’ Computer Management.
stripe
See “data striping”.
stripe size
The size of a data stripe (see data striping) on an
individual disk.
stripe width
The storage capacity of a data stripe (see data
striping) across all disks in an RAID. It is
calculated by multiplying the stripe size by the
number of disks that contain data that is neither
mirroring nor parity data. Therefore, for example,
in a four-disk RAID 0 (see RAID level) where the
stripe size is set to 128KB, the stripe width will
be 512KB (128KB x 4 disks = 512KB); however,
in a four-disk RAID 6 with a 128KB stripe size,
the stripe width is only 256KB because two of
the disks contain parity information.
subnet
A subnetwork, or subnet, is a logically visible
subdivision of a TCP/IP network. All computers
in a subnet have IP addresses with the same
prefix. Addresses in the same subnet are
reachable without going through a router, and
thus can be reached by broadcast.
subnet mask
A means of restricting IP addresses on a subnet
to a specific range.
syslog
System log. A standard for computer data
logging. It allows separation of the software that
generates messages from the system that
stores them and the software that reports and
analyzes them.
system reboot
On Nexsan storage systems, a method of
rebooting the unit’s RAID controllers. With this
method, both controllers are restarted at the
same time, which can interrupt host I/O. It is
therefore recommended that hosts be
disconnected or shut down before performing a
system reboot.
T
TB
Terabyte. Approximately one trillion
(1,000,000,000,000) bytes. Used to describe the
storage capacity of hard disk drives. A terabyte
is usually computed as 10^12
(1,000,000,000,000) bytes, but can also be
computed as 2^40 (1,099,511,627,776) bytes
Glossary
Nexsan High-Density Storage
User Guide
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