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Glossary
H
OT
S
WAP
— Replacement of a failed component while the system is running and
operating normally.
I
NITIALIZATION
— The process of writing zeros to the data fields of a virtual disk
and, in fault tolerant RAID levels, generating the corresponding parity to put the
virtual disk in a Ready state. Initialization generates parity information, so that the
virtual disk is redundant. Virtual disks can work without initialization, but they are not
truly redundant until initialization is performed.
INT 13
H
— A DOS interrupt used to activate seek, read, write and format disk
functions. The Int 13h interface supports physical disks that contain up to an
approximate maximum disk space of 8.45 GB.
JBOD (J
UST
A
B
UNCH
OF
D
ISKS
[D
RIVES
]) — A storage subsystem that uses a
single or multiple, independent disk drives.
LED (L
IGHT
E
MITTING
D
IODE
)—An electronic device that illuminates when
powered.
L
OAD
B
ALANCING
— Load balancing is a method of spreading work between two or
more computers, network links, CPUs, physical disk drives, or other resources. Load
balancing is used to maximize resource use, throughput, or response time. In the
controllers, the balancing service is performed by the firmware. You can choose
between a single path for load balancing, and a “round-robin” load balancing scheme.
In single path, the firmware can detect multiple paths to a device, and use only a single
path for I/O activity to that device. The secondary path is used if a failure is detected
on the primary path. If load balancing is enabled for the controller, the firmware
implements a round-robin scheme to issue I/Os to the redundant path device. The
round-robin scheme issues one I/O down one path, and the other I/O down the second
path, and so on. There is no restriction on firmware regarding which path to choose
first. If load balancing is disabled, the firmware can use any one of the available paths
to issue I/Os, and it should continue to use the same path for all further I/O activity.
On reboot or path failure, the firmware again chooses any available path.
MB — Acronym for megabyte(s). The term megabyte means 1,048,576 bytes (2^20
bytes); however, when referring to hard drive storage, the term is often rounded to
mean 1,000,000 bytes.
MIRRORING
— The process of providing complete redundancy using two physical
disks, by maintaining an exact copy of one physical disk’s data on the second physical
disk. If one physical disk fails, the contents of the other physical disk can be used to
maintain the integrity of the system and to rebuild the failed physical disk.
NAS (N
ETWORK
A
TTACHED
S
TORAGE
)—A server that runs an operating system for
handling files, and which is accessible directly on a LAN by using protocols like
TCP/IP.
A5_bk0.book Page 106 Thursday, February 10, 2011 8:34 PM