Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

Table 2-1
Tunable VxFS I/O parameters (continued)
DescriptionParameter
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
Any file I/O requests larger than
discovered_direct_iosz are handled as
discovered direct I/O. A discovered direct I/O is
unbuffered similar to direct I/O, but it does not require
a synchronous commit of the inode when the file is
extended or blocks are allocated. For larger I/O
requests, the CPU time for copying the data into the
page cache and the cost of using memory to buffer
the I/O data becomes more expensive than the cost
of doing the disk I/O. For these I/O requests, using
discovered direct I/O is more efficient than regular
I/O. The default value of this parameter is 256K.
discovered_direct_iosz
55VxFS performance: creating, mounting, and tuning file systems
Tuning I/O