Veritas File System 5.0 Administrator's Guide (September 2006)

Veritas Volume Manager maximum I/O size
When using VxFS with Veritas Volume Manager (VxVM), VxVM by default breaks
up I/O requests larger than 256K. When using striping, to optimize performance,
the file system issues I/O requests that are up to a full stripe in size. If the stripe
size is larger than 256K, those requests are broken up.
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 command to monitor free space is desirable.
See the df_vxfs(1M) manual page.
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.
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:
VxFS performance: creating, mounting, and tuning file systems
Monitoring free space
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