VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Tuning VxVM
292 VERITAS Volume Manager Administrator’s Guide
Number of Configuration Copies for a Disk Group
Selection of the number of configuration copies for a disk group is based on a trade-off
between redundancy and performance. As a general rule, reducing the number
configuration copies in a disk group speeds up initial access of the disk group, initial
startup of the vxconfigd daemon, and transactions performed within the disk group.
However, reducing the number of configuration copies also increases the risk of complete
loss of the configuration database, which results in the loss of all objects in the database
and of all data in the disk group.
The default policy for configuration copies in the disk group is to allocate a configuration
copy for each controller identified in the disk group, or for each target that contains
multiple addressable disks. This provides a sufficient degree of redundancy, but can lead
to alarge number of configuration copies undersome circumstances. If this isthe case,we
recommended that you limit the number of configuration copies to a minimum of 4.
Distribute the copies across separate controllers or targets to enhance the effectiveness of
this redundancy.
To setthe numberof configuration copiesfor anew disk group, use the nconfig operand
with the vxdg init command (see the vxdg(1M) manual page for details).
You can also change the number of copies for an existing group by using the vxedit set
command (see the vxedit(1M) manual page). For example, to configure five
configuration copies for the disk group, bigdg, use the following command:
# vxedit set nconfig=5 bigdg
Changing Values of Tunables
Tunables are modified by adding a line to /stand/system file. Changed tunables take
effect only after relinking the kernel and booting the system from the new kernel.
Modify tunables in /stand/system using the following format:
tunable value
Thevaluesofsystem tunables canbeexamined by selecting Kernel Configuration >
Configuration Parameters in the System Administration Manager (SAM).