VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9 409
The Number of Configuration Copies for a Disk Group
Selection of the number of configuration copies for a disk group is based
on the trade-off between redundancy and performance. As a general rule,
the fewer configuration copies that exist in a disk group, the quicker the
group can be initially accessed, the faster the initial start of the
vxconfigd(1M) command can proceed, and the quicker transactions can
be performed on the disk group.
CAUTION The risk of lower redundancy of the database copies is the loss of the
configuration database. Loss of the database results in the loss of all
objects in the database and all data contained 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 containing multiple addressable disks on the same target.
This is sufficient from the redundancy perspective, but can lead to large
numbers of configuration copies under some circumstances.
If this is the case, it is recommended to limit the number of configuration
copies to a minimum of 4. The location of the copies is selected as before,
according to maximal controller or target spread.
The mechanism for setting the number of copies for a disk group is to use
the vxdg init command for a new group setup (see the vxdg(1M)
manual page for details). Also, you can change copies of an existing
group by using the vxedit set command (see the vxedit(1M) manual
page for details). For example, to set a disk group called foodg to contain
5 copies, use the following command:
# vxedit set nconfig=5 foodg