VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Performance Monitoring and Tuning
Performance Monitoring
Chapter 12396
# vxplex -o rm dis archive-01
After reorganizing any particularly busy volumes, check the disk
statistics. If some volumes have been reorganized, clear statistics first
and then accumulate statistics for a reasonable period of time.
If some disks appear to be excessively busy (or have particularly long
read or write times), you may want to reconfigure some volumes. If there
are two relatively busy volumes on a disk, move them closer together to
reduce seek times on the disk. If there are too many relatively busy
volumes on one disk, move them to a disk that is less busy.
Use I/O tracing (or subdisk statistics) to determine whether volumes
have excessive activity in particular regions of the volume. If the active
regions can be identified, split the subdisks in the volume and move
those regions to a less busy disk.
CAUTION Striping a volume, or splitting a volume across multiple disks, increases
the chance that a disk failure results in failure of that volume. For
example, if five volumes are striped across the same five disks, then
failure of any one of the five disks requires that all five volumes be
restored from a backup. If each volume were on a separate disk, only one
volume would need to be restored. Use mirroring or RAID-5 to reduce the
chance that a single disk failure results in failure of a large number of
volumes.
Note that file systems and databases typically shift their use of allocated
space over time, so this position-specific information on a volume is often
not useful. Databases are reasonable candidates for moving to non-busy
disks if the space used by a particularly busy index or table can be
identified.
Examining the ratio of reads to writes helps to identify volumes that can
be mirrored to improve their performance. If the read-to-write ratio is
high, mirroring can increase performance as well as reliability. The ratio
of reads to writes where mirroring can improve performance depends
greatly on the disks, the disk controller, whether multiple controllers can
be used, and the speed of the system bus. If a particularly busy volume
has a high ratio of reads to writes, it is likely that mirroring can
significantly improve performance of that volume.