VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
Monitoring Free Space
Chapter 256
• Less than 5 percent of free space in extents of less than 64 blocks in length
• More than 5 percent of the total file system size available as free extents in lengths of 64
or more blocks
A badly fragmented file system will have one or more of the following characteristics:
• Greater than 5 percent of free space in extents of less than 8 blocks in length
• More than 50 percent of free space in extents of less than 64 blocks in length
• Less than 5 percent of the total file system size available as free extents in lengths of 64 or
more blocks
The optimal period for scheduling of 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 is approaching the figures for bad fragmentation, reduce the interval between
fsadm runs. If the degree of fragmentation is low, increase the interval between fsadm runs.
The “after” result is an indication of how well the reorganizer has performed. The degree of
fragmentation should be close to the characteristics of an unfragmented file system. If not, it
may be a good idea to resize the file system; full file systems tend to fragment and are difficult
to defragment. It is also possible that the reorganization is not being performed at a time
during which the file system in question is relatively idle.
Directory reorganization is not nearly as critical as extent reorganization, but regular
directory reorganization will improve performance. It is advisable to schedule directory
reorganization for file systems when the extent reorganization is scheduled. The following is a
sample script that is run periodically at 3:00 A.M. from cron for a number of file systems:
outfile=/usr/spool/fsadm/out.‘/bin/date +’%m%d’‘
for i in /home /home2 /project /db
do
/bin/echo "Reorganizing $i"
/bin/timex fsadm -F vxfs -e -E -s $i
/bin/timex fsadm -F vxfs -s -d -D $i
done > $outfile 2>&1