Veritas File System 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

Table 2-1
Tunable VxFS I/O parameters (continued)
DescriptionParameter
Increases or decreases the maximum size of an extent.
When the file system is following its default allocation
policy for sequential writes to a file, it allocates an initial
extent which is large enough for the first write to the file.
When additional extents are allocated, they are
progressively larger because the algorithm tries to double
the size of the file with each new extent. As such, each
extent can hold several writes worth of data. This is done
to reduce the total number of extents in anticipation of
continued sequential writes. When the file stops being
written, any unused space is freed for other files to use.
Normally this allocation stops increasing the size of
extents at 2048 blocks which prevents one file from
holding too much unused space.
max_seqio_extent_size is measured in file system
blocks. The default and minimum value of
max_seqio_extent_size is 2048.
max_seqio_extent_size
On VxFS, files can have up to ten direct extents of variable
size stored in the inode. After these extents are used up,
the file must use indirect extents which are a fixed size
that is set when the file first uses indirect extents. These
indirect extents are 8K by default. The file system does
not use larger indirect extents because it must fail a write
and return ENOSPC if there are no extents available that
are the indirect extent size. For file systems with many
large files, the 8K indirect extent size is too small. The
files that get into indirect extents use many smaller
extents instead of a few larger ones. By using this
parameter, the default indirect extent size can be
increased so large that files in indirects use fewer larger
extents. The tunable default_indir_ size should be
used carefully. If it is set too large, then writes fail when
they are unable to allocate extents of the indirect extent
size to a file. In general, the fewer and the larger the files
on a file system, the larger the default_indir_ size
can be set. This parameter should generally be set to some
multiple of the read_pref_io parameter.
default_indir_ size is not applicable on Version 4
disk layouts.
default_indir_ size
VxFS performance: creating, mounting, and tuning file systems
Tuning I/O
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