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Striping
Disk striping writes data across all physical disks in a
virtual disk. Each stripe consists of consecutive virtual
disk data addresses that are mapped in fixed-size units
to each physical disk in the virtual disk using a
sequential pattern. For example, if the virtual disk
includes five physical disks, the stripe writes data to
physical disks one through five without repeating any
of the physical disks. The amount of space consumed
by a stripe is the same on each physical disk. The
portion of a stripe that resides on a physical disk is a
stripe element. Striping by itself does not provide data
redundancy. Striping in combination with parity does
provide data redundancy.
T
TBBU
Acronym for Transportable Battery Backup Unit. The
TBBU protects the integrity of the cached data on the
controller by providing backup power if there is a
complete AC power failure or a brief power outage.
A transportable battery backup unit can be used to
move a controller's cached data that has not been
written to the disk to a replacement controller. After
you install the transportable battery backup unit on
the new controller, it flushes the unwritten data
preserved in the cache to the disk through the
new controller.
V
Virtual Disk
A virtual disk refers to storage created by a RAID
controller from one or more physical disks. Although a
virtual disk may be created from several physical disks,
it is seen by the operating system as a single disk.
Depending on the RAID level used, the virtual disk
may retain redundant data in case of a disk failure.
108
Glossary
W
Write-Back
In write-back caching mode, the controller sends a
data transfer completion signal to the host when the
controller cache has received all the data in a disk
write transaction. Data is written to the disk
subsystem in accordance with policies set up by the
controller. These policies include the amount of
dirty/clean cache lines, the number of cache lines
available, elapsed time from the last cache flush, and
others.
Write-Through
In write-through caching mode, the controller sends a
data transfer completion signal to the host when the
disk subsystem has received all the data and has
completed the write transaction to the disk.
X
XP
XP is a Microsoft Windows operating system.
Released in 2001, it is built on the Windows 2000
kernel, making it more stable and reliable than
previous versions of Windows. It includes an
improved user interface and more mobility features,
such as plug and play features used to connect to
wireless networks.
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