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

Chapter 3 77
Extent Attributes
Attribute Specifics
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 mkfs_vxfs(1M) and
Chapter 6 , “Application Interface” 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 will cause the file system to return an
error message reporting insufficient space if no suitably sized (or
aligned) extent is available. This may happen even if the file system has
plenty of 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.