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

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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 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.
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
quotas file and internal quotas file .
file system block The fundamental minimum size of allocation in a
file system. This is equivalent to the HFS fragment size.
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.
GB Gigabyte (230 bytes or 1024 megabytes).
hard limit The hard limit is an absolute limit on system resources for
individual users for file and data block usage on a file system. See quota .
I/O clustering The grouping of multiple I/O operations to achieve
better performance.
indirect address extent An extent that contains references to other
extents, as opposed to file data itself. A single indirect address extent
references indirect data extents. A double indirect address extent
references single indirect address extents.