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Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices

4.7 Tuning Using Array Performance Data

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.

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.

December 2008 – Revision A01

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