VERITAS Volume Manager 4.1 Administrator's Guide

Performance Monitoring and Tuning
Tuning VxVM
Chapter 12410
vol_max_vol
The maximum number of volumes that can be created on the system.
This value can be set to between 1 and the maximum number of minor
numbers representable in the system.
The default value for this tunable is 16777215.
vol_maxio
The maximum size of logical I/O operations that can be performed
without breaking up the request. I/O requests to VxVM that are larger
than this value are broken up and performed synchronously. Physical I/O
requests are broken up based on the capabilities of the disk device and
are unaffected by changes to this maximum logical request limit.
The default value for this tunable is 256 sectors (256KB).
NOTE The value of voliomem_maxpool_sz must be at least 10 times greater
than the value of vol_maxio.
vol_maxioctl
The maximum size of data that can be passed into VxVM via an ioctl
call. Increasing this limit allows larger operations to be performed.
Decreasing the limit is not generally recommended, because some
utilities depend upon performing operations of a certain size and can fail
unexpectedly if they issue oversized ioctl requests.
The default value for this tunable is 32768 bytes (32KB).
vol_maxkiocount
The maximum number of I/O operations that can be performed by VxVM
in parallel. Additional I/O requests that attempt to use a volume device
are queued until the current activity count drops below this value.
The default value for this tunable is 2048.
Because most process threads can only issue a single I/O request at a
time, reaching the limit of active I/O requests in the kernel requires 2048
I/O operations to be performed in parallel. Raising this limit is unlikely
to provide much benefit except on the largest of systems.