Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Extent Attributes
Attribute Specifics
Chapter 356
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 59 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.