Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

See the fsadm_vxfs(1M) manual page.
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 command.
To determine the degree of fragmentation, use the following factors:
■ Percentage of free space in extents of less than 8 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 has the following characteristics:
■ Less than 1 percent of free space in extents of less than 8 blocks in length
■ 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 has 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
VxFS performance: creating, mounting, and tuning file systems
Monitoring free space
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