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independent disk spindles. The amount of data written on each disk before moving to the
next drive is the stripe width.
terminator A part used to end a SCSI bus. Terminators prevent energy from reflecting back into a
cable plant by absorbing the radio frequency signals.
throughput A measure of sequential I/O performance, quoted in MB/sec. See IOPS.
Ultra160 SCSI
LVD
Ultra 3 SCSI command set plus a raw data rate of 160 MB/sec. plus the ability to connect
up to a distance of 12m (Low Voltage Differential)
volume Also called a logical unit number or LUN, a volume is one or more drives that can be
grouped into a unit for data storage. In VERITAS Volume Manager software, a volume is
a virtual disk partition into which a file system, DBMS, or other application can place
data. A volume can physically be a single disk partition or multiple disk partitions on one
or more physical disk drives. Applications that use volumes do not need to be aware of
their underlying physical structure. The VERITAS Volume Manager software handles
mapping of virtual partition addresses to physical addresses.
warm plug The ability to remove, replace or add a device while power is still applied but all I/O
processes are suspended.
write policy A cache-writing strategy used to control write operations. The write policy options are
write-back and write-through cache.
write-back cache A cache-writing strategy in which the array controller receives the data to be written to
disk, stores it in the memory buffer, and immediately sends the host operating
environment a signal that the write operation is complete, without waiting until the data is
actually written to the disk drive. Within a short time, the controller, when not busy,
writes the data to the disk drive. Write-back caching improves the performance of write
operations and the throughput of the controller card. However, because there is a danger
of data loss in the case of a power failure, arrays with write-back caching should be
equipped with a UPS or battery backup cache. A UPS will provide power long enough to
allow any data in the cache memory to be written to the disk drive. With battery backup
cache, the battery will provide power to retain the memory data for up to 48 hours.
write-through
cache
A cache-writing strategy in which the array controller writes the data to the disk drive
before signaling the host operating environment that the process is complete. Write-
through cache has lower write operation and throughput performance than write-back
cache, but it is the safer strategy, with minimum risk of data loss on power failure.
WWN Worldwide Name. A number used to identify array logical drives in both the array
software and in Solaris operating environment.
XOR eXclusive OR. A binary mathematical operation performed on data to produce parity
information. In RAID levels 3 and 5, parity is generated from the user data, stored, and
used to regenerate lost data if a drive failure occurs.