VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Tuning VxFS Prerelease 8 September 2005, 8:55am
404 VERITAS Storage Foundation for Oracle Administrator’s Guide
Tuning VxFS
VERITAS File System provides a set of tuning options to optimize file system performance for
different application workloads. VxFS provides a set of tunable I/O parameters that control some of
its behavior. These I/O parameters 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 largest benefit from tuning the file system.
Most of these tuning options have little or no impact on database performance when using Quick
I/O, with the exception of the max_thread_proc parameter. Other than setting the
max_thread_proc parameter (see “max_thread_proc” on page 416), use the general VxFS
defaults when creating a VxFS file system for databases. However, you can gather file system
performance data when using Quick I/O, and use this information to adjust the system
configuration to make the most efficient use of system resources.
Monitoring Free Space
In general, VxFS works best if the percentage of free space in the file system is greater than 10
percent. This is because file systems with 10 percent or more of free space have less fragmentation
and better extent allocation. Regular use of the df command to monitor free space is desirable. Full
file systems may have an adverse effect on file system performance. Full file systems should
therefore have some files removed or should be expanded. See the fsadm_vxfs(1M) manual
page for a description of online file system expansion.
Monitoring Fragmentation
Fragmentation reduces performance and availability. Regular use of fsadm’s fragmentation
reporting and reorganization facilities is therefore advisable.
The easiest way to ensure that fragmentation does not become a problem is to schedule regular
defragmentation runs using the cron command.
Defragmentation scheduling should range from weekly (for frequently used file systems) to
monthly (for infrequently used file systems). Extent fragmentation should be monitored with
fsadm or the df -o s commands. There are three factors that can be used to determine the degree
of fragmentation:
◆ Percentage of free space in extents that are less than eight blocks in length
◆ Percentage of free space in extents that are less than 64 blocks in length
◆ Percentage of free space in extents that are 64 or more blocks in length
An unfragmented file system will have the following characteristics:
◆ Less than 1 percent of free space in extents that are less than eight blocks in length
◆ Less than 5 percent of free space in extents that are less than 64 blocks in length