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483Performance monitoring and tuning
Tuning VxVM
voliomem_maxpool_sz
The maximum memory requested from the system by VxVM for internal
purposes. This tunable has a direct impact on the performance of VxVM as it
prevents one I/O operation from using all the memory in the system.
VxVM allocates two pools that can grow up to voliomem_maxpool_sz, one for
RAID-5 and one for mirrored volumes.
A write request to a RAID-5 volume that is greater than
voliomem_maxpool_sz/10 is broken up and performed in chunks of size
voliomem_maxpool_sz/10.
A write request to a mirrored volume that is greater than
voliomem_maxpool_sz/2 is broken up and performed in chunks of size
voliomem_maxpool_sz/2.
The default value for this tunable is 4M.
Note: The value of voliomem_maxpool_sz must be at least 10 times greater
than the value of vol_maxio.
voliot_errbuf_dflt
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 VxVM is
running.
The default size for this buffer is 16384 bytes (16KB).
Increasing this buffer can provide storage for more error events at the expense
of system memory. Decreasing the size of the buffer can result in an error not
being detected via the tracing device. Applications that depend on error tracing
to perform some responsive action are dependent on this buffer.
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