About monitoring fragmentation<a class="indexterm" name="id437153"></a><a class="indexterm" name="id437160"></a>


About monitoring fragmentation
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About 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 fsadmcommand.

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
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.