VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9 405
region.
The Volume Manager kernel currently sets the default value for this
tunable to 1024 sectors.
Larger region sizes will tend to cause the cache hit-ratio for regions to
improve. This will improve the write performance, but it will also prolong
the recovery time.
voldrl_max_drtregs
This tunable specifies the maximum number of dirty regions that can
exist on the system at any time. This is a global value applied to the
entire system, regardless of how many active volumes the system has.
The default value for this tunable is 2048.
The tunable voldrl_max_dtregs can be used to regulate the worse-case
recovery time for the system following a failure. A larger value may
result in improved system performance at the expense of recovery time.
vol_maxparallelio
This tunable controls the number of I/O operations that the
vxconfigd(1M) daemon is permitted to request from the kernel in a
single VOL_VOLDIO_READ per VOL_VOLDIO_WRITE ioctl call.
The default value for this tunable is 256, and it is unlikely that it is
desirable to change this value.
vol_mvr_maxround
This value controls the granularity of the round-robin policy for reading
from mirrors. A read will be serviced by the same mirror as the last read
if its offset is within the number of sectors described by this tunable of
the last read.
The default for this value is 512 sectors (256K).
Increasing this value will cause less switches to alternate mirrors for
reading. This is desirable if the I/O being performed is largely sequential
with a few small seeks between I/Os. Large numbers of randomly
distributed volume reads are generally best served by reading from
alternate mirrors.