Dell PowerVault MD3000 - Manual (Page 14)

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices
December 2008 – Revision A01 Page 14
4.7 Tuning Using Array Performance Data
4.7.1 Collecting Performance Statistics
The stateCaptureData.txt and performanceStatistics.csv files, which are available
through the MDSM, Support tab as part of a Technical Support Bundle, provide
valuable statistical data in an easy-to-read format. The following section shows
some sample data from the stateCaptureData.txt file and suggested
configuration recommendations based on the performance considerations
outlined in the previous section.
Other useful information is available through the array profile. Open the MDSM
and select the Support tab – View Storage Array Profile.
Before collecting performance statistics, the I/O workload under test should be
first executed. This will ensure the validity of performance statistics as part of the
measure step of proper performance tuning.
Note : Figures shown below are from using the performance tool Iometer.
4.7.2 RAID Level
The stateCaptureData.txt file provides statistics in the read and writes
percentage columns to aid in selecting most appropriate RAID level. In Figure 2,
the small reads and writes I/O percentages provide information regarding the
distribution of the I/O types in the tested workload. This data is especially helpful
when utilizing Table 1 referenced on page 7 to determining the applications
current read/write mix. The RAID Level chosen can impact the I/O performance.
Generally, RAID 1/10 has the best overall performance, with the highest physical
disk cost. Use the I/O percent distribution and the average block size from the
collected data to aid in this determination. These fields can be found in the
highlighted regions of Figure 2 and Figure 3 for First and Second Generation
Firmware respectively. It should be noted that the values in these figures are in
block notation; block size for the specific virtual disk configuration is listed in the
stateCaptureData.txt file, and is almost always 512 bytes. The average received
I/O is not the I/O size the application uses but what the host sends, so while an
application may attempt to send larger I/Os, the host’s I/O stack may coalesce or
break up I/Os as appropriate. Please see the appropriate separate OS or HBA
documentation to determine these values.