HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

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Glossary
access control list (ACL) The information that identifies specific
users or groups and their access privileges for a particular file or
directory.
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.
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 performance, but carries the
risk of data loss if the system crashes before the data is flushed to disk.
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 .
contiguous file A file in which data blocks are physically adjacent on
the underlying media.
current usage table A table containing fileset information, such as
the number of blocks currently used by the fileset. Not used in the
Version 3 or 4 disk layout.
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 processof 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.