VERITAS Volume Manager 4.1 Administrator's Guide

Performance Monitoring and Tuning
Tuning VxVM
Chapter 12414
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.
volraid_minpool_sz
The initial amount of memory that is requested from the system by
VxVM for RAID-5 operations. The maximum size of this memory pool is
limited by the value of voliomem_maxpool_sz.
The default value for this tunable is 2048 sectors (2MB).