Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 15, Performance Monitoring and Tuning
Tuning VxVM
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voliot_iobuf_default
The default size for the creation of a tracing buffer in the absence of any other specification
of desired kernel buffer size as part of the trace ioctl.
The default size of this tunable is 8192 bytes (8KB).
If trace data is often being lost due to this buffer size being too small, then this value can
be tuned to a more generous amount.
voliot_iobuf_limit
The upper limit to the size of memory that can be used for storing tracing buffers in the
kernel. Tracing buffers are used by the VxVM kernel to store the tracing event records. As
trace buffers are requested to be stored in the kernel, the memory for them is drawn from
this pool.
Increasing this size can allow additional tracing to be performed at the expense of system
memory usage. Setting this value to a size greater than can readily be accommodated on
the system is inadvisable.
The default value for this tunable is 131072 bytes (128KB).
voliot_iobuf_max
The maximum buffer size that can be used for a single trace buffer. Requests of a buffer
larger than this size are silently truncated to this size. A request for a maximal buffer size
from the tracing interface results (subject to limits of usage) in a buffer of this size.
The default size for this buffer is 65536 bytes (64KB).
Increasing this buffer can provide for larger traces to be taken without loss for very
heavily used volumes. Care should be taken not to increase this value above the value for
the voliot_iobuf_limit tunable value.
voliot_max_open
The maximum number of tracing channels that can be open simultaneously. Tracing
channels are clone entry points into the tracing device driver. Each vxtrace process
running on a system consumes 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.