Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

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 of configuration copies in a disk group speeds up initial access of the disk
group, initial startup of the vxconfigd daemon, and transactions that are
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 a large number of configuration copies under some
circumstances. If this is the case, we recommended that you limit the number of
configuration copies to a maximum of 4. Distribute the copies across separate
controllers or targets to enhance the effectiveness of this redundancy.
To set the number of configuration copies for a new 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. For example, to configure five configuration copies for
the disk group, bigdg, use the following command:
# vxedit set nconfig=5 bigdg
See the vxedit(1M) manual page.
Changing the values of VxVM tunables
Tunables are modified by using SMH or the kctune utility. Changed tunables take
effect only after relinking the kernel and booting the system from the new kernel.
The values of system tunables can be examined by selecting Kernel Configuration
> Tunables in SMH.
DMP tunables are set online (without requiring a reboot) by using the vxdmpadm
command as shown here:
# vxdmpadm settune dmp_tunable=value
The values of these tunables can be displayed by using this command:
# vxdmpadm gettune [dmp_tunable]
495Performance monitoring and tuning
Tuning VxVM