Hitachi G1500 - Page 181

local area network (LAN)
A computer network that spans a r
elatively small geogr
aphic ar
ea, such as a single building or
gr
oup of buildings.
logical
Describes a user's view of the way data or systems are organized. The opposite of logical is
physical, which refers to the real organization of a system. A logical description of a le that it
is a quantity of data collected together in one place. The le appears this way to users.
Physically, the elements of the le could live in segments across a disk.
microcode
The lowest-level instructions directly controlling a microprocessor. Microcode is generally
hardwired and cannot be modied. It is also referred to as rmware embedded in a storage
subsystem.
Microsoft Cluster Server
A clustering technology that supports clustering of two NT servers to provide a single fault-
tolerant server.
pair
Two logical volumes in a replication relationship in which one volume contains original data to
be copied and the other volume contains the copy of the original data. The copy operations
can be synchronous or asynchronous, and the pair volumes can be located in the same
storage system (in-system replication) or in dierent storage systems (remote replication).
pair status
Indicates the condition of a copy pair. A pair must have a specic status for specic
operations. When a pair operation completes, the status of the pair changes to a dierent
status determined by the type of operation.
parity
In computers, parity refers to a technique of checking whether data has been lost or written
over when it is moved from one place in storage to another or when transmitted between
computers.
Parity computations are used in RAID drive arrays for fault tolerance by calculating the data in
two drives and storing the results on a third. The parity is computed by XOR'ing a bit from
drive 1 with a bit from drive 2 and storing the result on drive 3. After a failed drive is replaced,
the RAID controller rebuilds the lost data from the other two drives. RAID systems often have
a "hot" spare drive ready and waiting to replace a drive that fails.
parity group
See RAID group.
point-to-point
A topology where two points communicate.
port
An access point in a device where a link attaches.
Glossary
Hitachi Virtual Storage Platform G1000, G1500, and VSP F1500 Hardware Guide 181