Dell EMC PowerVault MD Series Administrator's Manual page 29

Performance Data
IOs/sec
MBs/sec
I/O Latency, ms
Implications for Performance Tuning
continue to meet application needs at an acceptable performance
level.
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 individual virtual disk, look at the current IOPS and the
maximum IOPS. You should see higher rates for sequential I/O
patterns than for random I/O patterns. Regardless of your I/O
pattern, enable write caching to maximize the I/O rate and to
shorten the application response time. For more information about
read/write caching and performance, see the related topics listed at
the end of this topic.
See IOs/sec.
Latency is useful for monitoring the I/O activity of a specific
physical disk and a specific virtual disk and can help you identify
physical disks that are bottlenecks.
Physical disk type and speed influence latency. With random I/O,
faster spinning physical disks spend less time moving to and from
different locations on the disk.
Too few physical disks result in more queued commands and a
greater period of time for the physical disk to process the
command, increasing the general latency of the system.
Larger I/Os have greater latency due to the additional time involved
with transferring data.
About your MD Series storage array 29