VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 14, Tuning for Performance
Prerelease 8 September 2005, 8:55am Tuning VxFS
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◆ More than 5 percent of the total file system size available as free extents that are 64 or more
blocks in length
A badly fragmented file system will have one or more of the following characteristics:
◆ More than 5 percent of free space in extents that are less than 8 blocks in length
◆ More than 50 percent of free space in extents that are less than 64 blocks in length
◆ Less than 5 percent of the total file system size available as free extents that are 64 or more
blocks in length
The optimal period for scheduling extent reorganization runs can be determined by choosing a
reasonable interval, scheduling fsadm runs at the initial interval, and running the extent
fragmentation report feature of fsadm before and after the reorganization.
The “before” result is the degree of fragmentation prior to the reorganization. If the degree of
fragmentation approaches the percentages for bad fragmentation, reduce the interval between
fsadm. If the degree of fragmentation is low, increase the interval between fsadm runs.
Tuning VxFS I/O Parameters
VxFS provides a set of tunable I/O parameters that control some of its behavior. These I/O
parameters are useful to help the file system adjust to striped or RAID-5 volumes that could yield
performance far superior to a single disk. Typically, data streaming applications that access large
files see the biggest benefit from tuning the file system.
If VxFS is being used with VERITAS Volume Manager, the file system queries VxVM to
determine the geometry of the underlying volume and automatically sets the I/O parameters.
VxVM is queried by mkfs when the file system is created to automatically align the file system to
the volume geometry. If the default alignment from mkfs is not acceptable, the -o align=n
option can be used to override alignment information obtained from VxVM. The mount command
also queries VxVM when the file system is mounted and downloads the I/O parameters.
If the default parameters are not acceptable or the file system is being used without VxVM, then the
/etc/vx/tunefstab file can be used to set values for I/O parameters. The mount command
reads the /etc/vx/tunefstab file and downloads any parameters specified for a file system.
The tunefstab file overrides any values obtained from VxVM. While the file system is
mounted, any I/O parameters can be changed using the vxtunefs command, which can have
tunables specified on the command line or can read them from the /etc/vx/tunefstab file.
For more details, see the vxtunefs(1M) and tunefstab(4) manual pages. The vxtunefs
command can be used to print the current values of the I/O parameters.