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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This tunable limits the size of an I/O request at a higher level in VxVM than the level of an
individual disk. For example, for an 8 by 64KB stripe, a value of 256KB only allows I/O
requests that use half the disks in the stripe; thus, it cuts potential throughput in half. If
you have more columns or you have used a larger interleave factor, then your relative
performance is worse.
This tunable must be set, as a minimum, to the size of your largest stripe (RAID-0 or
RAID-5).
vol_subdisk_num
The maximum number of subdisks that can be attached to a single plex. There is no
theoretical limit to this number, but it has been limited to a default value of 4096. This
default can be changed, if required.
volcvm_smartsync
If set to 0, volcvm_smartsync disables SmartSync on shared disk groups. If set to 1, this
parameter enables the use of SmartSync with shared disk groups. See“SmartSync
Recovery Accelerator” on page 44 for more information.
voldrl_max_drtregs
The maximum number of dirty regions that can exist on the system for non-sequential
DRL on volumes. A larger value may result in improved system performance at the
expense of recovery time. This tunable can be used to regulate the worse-case recovery
time for the system following a failure.
The default value for this tunable is 2048.
voldrl_max_seq_dirty
The maximum number of dirty regions allowed for sequential DRL. This is useful for
volumes that are usually written to sequentially, such as database logs. Limiting the
number of dirty regions allows for faster recovery if a crash occurs.
The default value for this tunable is 3.
voldrl_min_regionsz
The minimum number of sectors for a dirty region logging (DRL) volume region. With
DRL, VxVM logically divides a volume into a set of consecutive regions. Larger region
sizes tend to cause the cache hit-ratio for regions to improve. This improves the write
performance, but it also prolongs the recovery time.