VERITAS File System 4.1 Administrator's Guide

Glossary
data block
Glossary260
D
data block A block that contains the actual
data belonging to files and directories.
data synchronous writes A form of
synchronous I/O that writes the file data to
disk before the write returns, but only marks
the inode for later update. If the file size
changes, the inode will be written before the
write returns. In this mode, the file data is
guaranteed to be on the disk before the write
returns, but the inode modification times
may be lost if the system crashes.
defragmentation The process of
reorganizing data on disk by making file
data blocks physically adjacent to reduce
access times.
direct extent An extent that is referenced
directly by an inode.
direct I/O An unbuffered form of I/O that
bypasses the kernel’s buffering of data. With
direct I/O,the file system transfers data
directly between the disk and the
user-supplied buffer. See also buffered I/O
and unbuffered I/O.
discovered direct I/O Discovered Direct
I/O behavior is similar to direct I/O and has
the same alignment constraints, except
writes that allocate storage or extend the file
size do not require writing the inode changes
before returning to the application.
E
encapsulation A process that converts
existing partitions on a specified disk to
volumes. If any partitions contain file
systems, /etc/fstab entries are modified so
that the file systems are mounted on
volumes instead. Encapsulation is not
applicable on some systems.
extent A group of contiguous file system
data blocks treated as a single unit. An
extent is defined by the address of the
starting block and a length.
extent attribute A policy that determines
how a file allocates extents.
external quotas file A quotas file (named
quotas) must exist in the root directory of a
file system for quota-related commands to
work. See also quotas file and internal
quotas file..
F
file system block The fundamental
minimum size of allocation in a file system.
This is equivalent to the fragment size on
some UNIX file systems.
fileset A collection of files within a file
system.
fixed extent size An extent attribute used
to override the default allocation policy of
the file system and set all allocations for a
file to a specific fixed size.