Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

parity A calculated value that can be used to reconstruct data after a failure. While data
is being written to a RAID-5 volume, parity is also calculated by performing an
exclusive OR (XOR) procedure on data. The resulting parity is then written to the
volume. If a portion of a RAID-5 volume fails, the data that was on that portion
of the failed volume can be recreated from the remaining data and the parity.
partition The logical areas into which a disk is divided.
persistence Information or state that will survive a system reboot or crash.
petabyte A measure of memory or storage. A petabyte is approximately 1,000 terabytes
(technically, 2 to the 50th power).
plex A duplicate copy of a volume and its data (in the form of an ordered collection of
subdisks). Each plex is one copy of a volume with which the plex is associated.
The terms mirror and plex can be used synonymously.
preallocation Prespecifying space for a file so that disk blocks will physically be part of a file
before they are needed. Enabling an application to preallocate space for a file
guarantees that a specified amount of space will be available for that file, even if
the file system is otherwise out of space.
Quick I/O Quick I/O presents a regular Veritas File System file to an application as a raw
character device. This allows Quick I/O files to take advantage of asynchronous
I/O and direct I/O to and from the disk device, as well as bypassing the UNIX
single-writer lock behavior for most file system files.
Quick I/O file A regular UNIX file that is accessed using the Quick I/O naming extension
(::cdev:vxfs:).
RAID A Redundant Array of Independent Disks (RAID) is a disk array set up with part
of the combined storage capacity used for storing duplicate information about
the data stored in that array. This makes it possible to regenerate the data if a
disk failure occurs.
repository A repository holds the name, type, range of values, source, and authorization for
access for each data element in a database. The database maintains a repository
for administrative and reporting use.
Pertinent information, needed to display configuration information and interact
with the database, is stored in the repository.
root disk The disk containing the root file system.
root disk group A special private disk group on the system. The root disk group is named rootdg.
However, starting with the 4.1 release of Veritas Volume Manager, the root disk
group is no longer needed.
root file system The initial file system mounted as part of the UNIX kernel startup sequence.
script A file, containing one or more commands that can be run to perform processing.
541Glossary