VERITAS File System 4.1 Administrator's Guide

Extent Attributes
Attribute Specifics
Chapter 372
Other Controls
The auxiliary controls on extent attributes determine:
• Whether allocations are aligned
• Whether allocations are contiguous
• Whether the file can be written beyond its reservation
• Whether an unused reservation is released when the file is closed
• Whether the reservation is a persistent attribute of the file
• When the space reserved for a file will actually become part of the file
Alignment
Specific alignment restrictions coordinate a file’s allocations with a particular I/O pattern or
disk alignment (see the mkfs_vxfs (1M) manual page and “Application Interface” on page 75
for details). Alignment can only be specified if a fixed extent size has also been set. Setting
alignment restrictions on allocations is best left to well designed applications.
Contiguity
A reservation request can specify that its allocation remain contiguous (all one extent).
Maximum contiguity of a file optimizes its I/O characteristics.
NOTE Fixed extent sizes or alignment cause a file system to return an error message
reporting insufficient space if no suitably sized (or aligned) extent is available.
This can happen even if the file system has sufficient free space and the fixed
extent size is large.
Write Operations Beyond Reservation
A reservation request can specify that no allocations can take place after a write operation
fills up the last available block in the reservation. This specification can be used in a similar
way to ulimit to prevent a file’s uncontrolled growth.
Reservation Trimming
A reservation request can specify that any unused reservation be released when the file is
closed. The file is not completely closed until all processes open against the file have closed it.