VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9 407
expense of system memory. Decreasing the size of the buffer could lead to
a situation where an error cannot be detected via the tracing device.
Applications that depend on error tracing to perform some responsive
action are dependent on this buffer.
voliot_max_open
This value controls the maximum number of tracing channels that can
be open simultaneously. Tracing channels are clone entry points into the
tracing device driver. Each running vxtrace command on the system
will consume a single trace channel.
The default number of channels is 32. The allocation of each channel
takes up approximately 20 bytes even when not in use.
vol_checkpt_default
This tunable controls the interval at which utilities performing
recoveries or resynchronization operations will load the current offset
into the kernel such that a system failure will not require a full recovery,
but can continue from the last reached checkpoint.
The default value of the checkpoint is 20480 sectors (10M).
Increasing this size reduces the overhead of checkpointing on recovery
operations at the expense of additional recovery following a system
failure during a recovery.
volraid_rsrtransmax
This RAID-5 tunable controls the maximum number of transient
reconstruct operations that can be performed in parallel. A transient
reconstruct operation is one which occurs on a non-degraded RAID-5
volume and was thus not predicted. By limiting the number of these
operations that can occur simultaneously, the possibility of flooding the
system with many reconstruct operations at the same time is removed,
reducing the risk of causing memory starvation conditions.
The default number of these transient reconstructs that can be
performed in parallel is 1.
Increasing this size may improve the initial performance on the system
when a failure first occurs and before a detach of a failing object is
performed, but can lead to possible memory starvation conditions.