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Volume Migration cannot estimate DKP usage, and may not provide any
performance improvement for cases in which DKP usage values vary only
slightly or for cases in which overall DRR usage values are relatively high.
Volume Migration is designed for use with obvious cases of high or unbalanced
DKP usage. For information on using Volume Migration, contact the Hitachi
Data Systems Support Center (see Calling the Hitachi Data Systems Support
Center.
DRR Processor Usage Statistics
A data recovery and reconstruction processor (DRR) is a microprocessor
(located on the DKAs) that is used to generate parity data for RAID-5 or RAID-
6 parity groups. The DRR uses the formula "old data + new data + old parity"
to generate new parity.
If the monitor data shows high DRR usage overall, this can indicate high write
penalty condition. Please consult your Hitachi Data Systems representative
about high write penalty conditions. If the monitor data shows that DRR usage
is not balanced, you should consider relocating volumes using Volume
Migration to balance DRR usage within the storage system.
For information on using Volume Migration, contact the Hitachi Data Systems
Support Center (see Calling the Hitachi Data Systems Support Center.
For details on how to view usage statistics on DRRs, see Viewing Usage
Statistics on Data Recovery and Reconstruction Processors.
Write Pending Rate and Cache Memory Usage Statistics
The write pending rate indicates the ratio of write-pending data to the cache
memory capacity. The Performance Management window displays the
average and the maximum write pending rate for the specified period of time.
When you display monitoring results in a short range, the window also displays
the average and the maximum usage statistics about the cache memory for
the specified period of time. In addition, the window can display a graph that
indicates how the write pending rate or the usage statistics of the cache
memory changed within that period.
For details on how to view the write pending rate and the usage statistics
about the cache memory, see Viewing Write Pending and Cache Memory
Usage Statistics.
Hitachi Universal Storage Platform V/VM Hitachi Performance Manager User's Guide
About Performance Manager Options
2-9
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