VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9406
voliot_iobuf_limit
This value sets a limit to the size of memory that can be used for storing
tracing buffers in the kernel. Tracing buffers are used by the Volume
Manager 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 (128K).
voliot_iobuf_max
This value controls the maximum buffer size that can be used for a single
trace buffer. Requests of a buffer larger than this size will be silently
truncated to this size. A request for a maximal buffer size from the
tracing interface will result (subject to limits of usage) in a buffer of this
size.
The default size for this buffer is 65536 bytes (64K).
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_iobuf_default
This value is 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 (8K).
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_errbuf_default
This tunable contains the default size of the buffer maintained for error
tracing events. This buffer is allocated at driver load time and is not
adjustable for size while the Volume Manager is running.
The default size for this buffer is 16384 bytes (16K).
Increasing this buffer can provide storage for more error events at the