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

Tuning VxVM
412 VERITAS Volume Manager Administrator’s Guide
dmp_restore_daemon_policy
The DMP restore policy, which can be set to 0 (CHECK_ALL), 1 (CHECK_DISABLED), 2
(CHECK_PERIODIC), or 3 (CHECK_ALTERNATE).
dmp_retry_count
If an inquiry succeeds on a path, but there is an I/O error, the number of retries to attempt
on the path.
vol_checkpt_default
The interval at which utilities performing recoveries or resynchronization operations load
the current offset into the kernel as a checkpoint. A system failure during such operations
does not require a full recovery, but can continue from the last reached checkpoint.
The default value of the checkpoint is 10240 sectors (10MB).
Increasing this size reduces the overhead of checkpointing on recovery operations at the
expense of additional recovery following a system failure during a recovery.
vol_default_iodelay
The count in clock ticks for which utilities pause if they have been directed to reduce the
frequency of issuing I/O requests, but have not been given a specific delay time. This
tunable is used by utilities performing operations such as resynchronizing mirrors or
rebuilding RAID-5 columns.
The default for this tunable is 50 ticks.
Increasing this value results in slower recovery operations and consequently lower system
impact while recoveries are being performed.
vol_fmr_logsz
The maximum size in kilobytes of the bitmap that Non-Persistent FastResync uses to track
changed blocks in a volume. The number of blocks in a volume that are mapped to each
bit in the bitmap depends on the size of the volume, and this value changes if the size of
the volume is changed. For example, if the volume size is 1 gigabyte and the system block
size is 1024 bytes, a vol_fmr_logsz value of 4 yields a map contains 32,768 bits, each bit
representing one region of 32 blocks.
The larger the bitmap size, the fewer the number of blocks that are mapped to each bit.
This can reduce the amount of reading and writing required on resynchronization, at the
expense of requiring more non-pageable kernel memory for the bitmap. Additionally, on
clustered systems, a larger bitmap size increases the latency in I/O performance, and it