HP-UX Reference (11i v1 00/12) - 1M System Administration Commands N-Z (vol 4)

__________________________________________________________________________________________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________________________________________________________________________________________
STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man1m/naaagt.1m
________________________________________________________________
___ ___
v
vxtunefs(1M) vxtunefs(1M)
NAME
vxtunefs - tune a VxFS File System
SYNOPSIS
/sbin/vxtunefs [-ps][-f tunefstab][-o parameter=value][{mount_point|block_special}]...
DESCRIPTION
vxtunefs sets or prints tuneable I/O parameters of mounted file systems. vxtunefs can set parame-
ters describing the I/O properties of the underlying device, parameters to indicate when to treat an I/O as
direct I/O, or parameters to control the extent allocation policy for the specified file system.
With no options specified, vxtunefs prints the existing VxFS parameters for the specified file systems.
vxtunefs works on a list of mount points specified on the command line, or all the mounted file systems
listed in the tunefstab file. The default tunefstab file is /etc/vx/tunefstab. You can change
the default using the -f option.
vxtunefs can be run at any time on a mounted file system, and all parameter changes take immediate
effect. Parameters specified on the command line override parameters listed in the tunefstab file.
If /etc/vx/tunefstab
exists, the VxFS-specific
mount command invokes vxtunefs to set device
parameters from
/etc/vx/tunefstab
.
Options
-f filename
Use filename instead of /etc/vx/tunefstab
as the file containing tuning parameters.
-o parameter=value
Specify parameters for the file systems listed on the command line. The parameters are listed
below.
-p Print the tuning parameters for all the file systems specified on the command line.
-s Set the new tuning parameters for the VxFS file systems specified on the command line or in the
tunefstab file.
VxFS Tuning Parameters and Guidelines
The values for all the following parameters except read_nstream and write_nstream
can be
specified in bytes, kilobytes, megabytes or sectors (512 bytes) by appending
k, K,
m, M, s,orS. There is no
need for a suffix for the value in bytes.
For an application to do efficient direct I/O or discovered direct I/O, it should issue read requests that are
equal to the product of
read_nstream and read_pref_io . In general, any multiple or factor of
read_nstream multiplied by read_pref_io is a good size for performance. For writing, the same
general rule applies to the write_pref_io
and write_nstream parameters. When tuning a file sys-
tem, the best thing to do is use the tuning parameters under a real workload.
If an application is doing sequential I/O to large files, it should issue requests larger than the
discovered_direct_iosz. This performs the I/O requests as discovered direct I/O requests which
are unbuffered like direct I/O, but which do not require synchronous inode updates when extending the file.
If the file is too large to fit in the cache, using unbuffered I/O avoids losing useful data out of the cache, and
lowers CPU overhead.
The VxFS tuneable parameters are:
default_indir_size
On VxFS, files can have up to 10 variable sized extents stored in the inode. After these extents are
used, 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 a lot of smaller extents instead of a few larger ones.
By using this parameter, the default indirect extent size can be increased so that large files in
indirects use fewer larger extents.
Be careful using this tuneable. If it is 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 sys-
tem, the larger default_indir_size
can be. The value of this parameter is generally a multiple
HP-UX Release 11i: December 2000 − 1 − Section 1M−−1057
___
___