VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 12, Performance Monitoring and Tuning
Tuning VxVM
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voldrl_max_drtregs
The maximum number of dirty regions that can exist for non-sequential DRL on a
volume. 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 sectors (2MB).
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
regionsizes tend tocause thecache hit-ratio forregionsto improve.This improvesthe
write performance, but it also prolongs the recovery time.
The VxVM kernel currently sets the default value for this tunable to 512 sectors.
voliomem_chunk_size
The granularity of memory chunks used by VxVM when allocating or releasing
system memory. A larger granularity reduces CPU overhead due to memory
allocation by allowing VxVM to retain hold of a larger amount of memory.
The default size for this tunable is 64KB.
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 requestto aRAID-5volume thatisgreaterthan voliomem_maxpool_sz/10
is broken up and performed in chunks of size voliomem_maxpool_sz/10.