VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9402
Tuning the Volume Manager
This section describes the mechanisms for controlling the resources used
by the Volume Manager. Adjustments may be required for some of the
tunable values to obtain best performance (depending on the type of
system resources available).
General Tuning Guidelines
The Volume Manager is tuned for most configurations ranging from
small systems to larger servers. In cases where tuning can be used to
increase performance on larger systems at the expense of a valuable
resource (such as memory), the Volume Manager is generally tuned to
run on the smallest supported configuration. These tuning changes
should be performed with care as they may adversely affect overall
system performance or may even leave the Volume Manager unusable.
Various mechanisms exist for tuning the Volume Manager. On some
systems, several parameters can be tuned using the global tunable file
/stand/system. Other values can only be tuned using the command line
interface to the Volume Manager.
Tunables
In many cases, tunables are contained in the volinfo structure, as
described in the vxio(7) manual page. 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 with the following format:
# tunable tunable_values
The sections that follow describe specific tunables.
vol_maxvol
This value controls the maximum number of volumes that can be created
on the system. This value can be set to between 1 and the maximum
number of minor numbers representable in the system.
The default value for this tunable is half the value of the maximum
minor number value on the system.