Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 15, Performance Monitoring and Tuning
Tuning VxVM
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also increases the load on the private network between the cluster members. This is
because every other member of the cluster must be informed each time a bit in the map is
marked.
Since the region size must be the same on all nodes in a cluster for a shared volume, the
value of the vol_fmr_logsz tunable on the master node overrides the tunable values on
the slave nodes, if these values are different. Because the value of a shared volume can
change, the value of vol_fmr_logsz is retained for the life of the volume.
In configurations which have thousands of mirrors with attached snapshot plexes, the
total memory overhead can represent a significantly higher overhead in memory
consumption than is usual for VxVM.
The default value of this tunable is 4KB. The maximum and minimum permitted values
are 1KB and 8KB.
Note The value of this tunable does not have any effect on Persistent FastResync.
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.
If DRL sequential logging is configured, the value of voldrl_min_regionsz
must be set to at least half the value of vol_maxio.