Dell PowerVault MD3820f - Manual (Page 36)

Performance Data Implications for Performance Tuning
You might notice a disparity in the total I/Os
(workload) of RAID controller modules. For
example, the workload of one RAID controller
module is heavy or is increasing over time while
that of the other RAID controller module is lighter
or more stable. In this case, you might want to
change the RAID controller module ownership of
one or more virtual disks to the RAID controller
module with the lighter workload. Use the virtual
disk total I/O statistics to determine which virtual
disks to move.
You might want to monitor the workload across
the storage array. Monitor the Total I/Os in the
background performance monitor. If the workload
continues to increase over time while application
performance decreases, you might need to add
additional storage arrays. By adding storage arrays
to your enterprise, you can continue to meet
application needs at an acceptable performance
level.
IOs/sec Factors that affect input/output operations per
second (IOs/sec or IOPS) include these items:
• Access pattern (random or sequential)
• I/O size
• RAID level
• Cache block size
• Whether read caching is enabled
• Whether write caching is enabled
• Dynamic cache read prefetch
• Segment size
• The number of physical disks in the disk groups
or storage array
The transfer rates of the RAID controller module
are determined by the application I/O size and the
I/O rate. Generally, small application I/O requests
result in a lower transfer rate but provide a faster
I/O rate and shorter response time. With larger
application I/O requests, higher throughput rates
are possible. Understanding your typical
application I/O patterns can help you determine
the maximum I/O transfer rates for a specific
storage array.
You can see performance improvements caused
by changing the segment size in the IOPS statistics
for a virtual disk. Experiment to determine the
optimal segment size, or use the file system size or
database block size. For more information about
segment size and performance, see the related
topics listed at the end of this topic.
The higher the cache hit rate, the higher I/O rates
will be. Higher write I/O rates are experienced with
write caching enabled compared to disabled. In
deciding whether to enable write caching for an
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