HP Veritas Volume Manager 5.0 -UX 11i v3 Dmpstatinterval, Volcheckptdefault, Voldefaultiodelay

Performance monitoring and tuning

Tuning VxVM

479

dmp_stat_interval

The time interval between gathering DMP statistics. The default and minimum value is 1 second.

The value of this tunable is changed by using the vxdmpadm settune command.

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 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.