VERITAS File System 4.1 Administrator's Guide

Glossary
Unbuffered I/O
Glossary 263
quotas file The quotas commands read and
write the external quotas file to get or
change usage limits. When quotas are
turned on, the quota limits are copied from
the external quotas file to the internal
quotas file. See also quotas, internal quotas
file, and external quotas file..
R
reservation An extent attribute used to
preallocate space for a file.
root disk group A special private disk
group that always exists on the system. The
root disk group is named rootdg.
S
shared disk group A disk group in which
the disks are shared by multiple hosts (also
referred to as a cluster-shareable disk
group).
shared volume A volume that belongs to a
shared disk group and is open on more than
one node at the same time.
snapshot file system An exact copy of a
mounted file system at a specific point in
time. Used to do online backups.
snapped file system A file system whose
exact image has been used to create a
snapshot file system.
soft limit The soft limit is lower than a hard
limit. The soft limit can be exceeded for a
limited time. There are separate time
limits for files and blocks. See also hard
limit and quota..
Storage Checkpoint A facility that
provides a consistent and stable view of a file
system or database image and keeps track of
modified data blocks since the last Storage
Checkpoint.
structural fileset The files that define the
structure of the file system. These files are
not visible or accessible to the user.
super-block A block containing critical
information about the file system such as the
file system type, layout, and size. The VxFS
super-block is always located 8192 bytes
from the beginning of the file system and is
8192 bytes long.
synchronous writes A form of
synchronous I/O that writes the file data to
disk, updates the inode times, and writes the
updated inode to disk. When the write
returns to the caller, both the data and the
inode have been written to disk.
T
TB Terabyte (240 bytes or 1024 gigabytes).
transaction Updates to the file system
structure that are grouped together to
ensure they are all completed
throughput For file systems, this typically
refers to the number of I/O operations in a
given unit of time.
U
Unbuffered I/O I/O that bypasses the
kernel cache to increase I/O performance.
This is similar to direct I/O, except when a