VERITAS File System 4.1 Administrator's Guide

Glossary 259
Glossary
A
Acess Control Lists The information that
identifies specific users or groups and their
access privileges for a particular file or
directory.
agent A process that manages predefined
VERITAS Cluster Server (VCS) resource
types. Agents bring resources online, take
resources offline, and monitor resources to
report any state changes to VCS. When an
agent is started, it obtains configuration
information from VCS and periodically
monitors the resources and updates VCS
with the resource status.
allocation unit A group of consecutive
blocks on a file system that contain resource
summaries, free resource maps, and data
blocks. Allocation units also contain copies of
the super-block.
API Application Programming Interface.
asynchronous writes A delayed write in
which the data is written to a page in the
system’s page cache, but is not written to
disk before the write returns to the caller.
This improves per formance, but carries the
risk of data loss if the system crashes before
the data is flushed to disk.
atomic operation An operation that either
succeeds completely or fails and leaves
everything as it was before the operation
was started. If the operation succeeds, all
aspects of the operation take effect at once
and the intermediate states of change are
invisible. If any aspect of the operation fails,
then the operation aborts without leaving
partial changes.
B
Block-Level Incremental Backup (BLI
Backup) A VERITAS backup capability
that does not store and retrieve entire files.
Instead, only the data blocks that have
changed since the previous backup are
backed up.
buffered I/O During a read or write
operation, data usually goes through an
intermediate kernel buffer before being
copied between the user buffer and disk. If
the same data is repeatedly read or written,
this kernel buffer acts as a cache, which can
improve performance. See unbuffered I/O
and direct I/O.
C
CFS VERITAS Cluster File System.
cluster mounted file system A shared file
system that enables multiple hosts to mount
and perform file operations on the same file.
A cluster mount requires a shared storage
device that can be accessed by other cluster
mounts of the same file system. Writes to the
shared device can be done concurrently from
any host on which the cluster file system is
mounted. To be a cluster mount, a file
system must be mounted using the mount -o
cluster option. See also local mounted file
system.
contiguous file A file in which data blocks
are physically adjacent on the underlying
media.
CVM The cluster functionality of VERITAS
Volume Manager.