HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

102 Chapter5
Performance and Tuning
Monitoring Free Space
Monitoring Free Space
In general, VxFS works best if the percentage of free space in the file
system does not get below 10 percent. This is because file systems with
10 percent or more free space have less fragmentation and better extent
allocation. Regular use of the df_vxfs(1M) 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 fsadm_vxfs(1M)for a description of
online file system expansion).
NOTE The reorganization and resize features of fsadm_vxfs(1M) are available
only with the optional HP OnLineJFS product.
Monitoring Fragmentation
Fragmentation reduces performance and availability. Regular use of
fsadm’sfragmentation 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 from cron.
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_vxfs(1M) or the -o s
options of df_vxfs(1M). There are three factors which can be used to
determine the degree of fragmentation:
• percentage of free space in extents of less than eight blocks in length
• percentage of free space in extents of less than 64 blocks in length
• percentage of free space in extents of length 64 blocks or greater
An unfragmented file system will have the following characteristics:
• less than 1 percent of free space in extents of less than eight blocks in
length
• less than 5 percent of free space in extents of less than 64 blocks in