Dell PowerVault MD3000i Dell PowerVault MD3000/MD3000i Array Tuning Best Pract - Page 18

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices In addition, the stateCaptureData.txt file provides a more granular method for determining the distribution of I/O within stripes and segments. In Figure 7 and Figure 8, item 1 is the number of full stripes read and written, and item 2 indicates the number of full clusters or segments read or written. The value of stripes per I/O request within reads and writes is also valuable for determining if stripe or segment settings are optimal for the tested data access pattern. The second generation firmware does not specifically break out the per-I/O ratio in data output as the first generation firmware did, however it can still be manually calculated simply by dividing the value in item 1 or 2 by the appropriate I/O request value from item 3 indicated in Figure 8. In most cases, best performance is achieved with segment and stripe per-I/O ratios as close to 1.00. Traditionally, when tuning for maximal I/Os per second, if the segments per-I/O ratio is high, the current segment size may be too low for the application. Similarly, when tuning for highest possible data transfer rate, the stripe per-I/O ratio should ideally be 1.00 or even multiples. If this value is high, increasing the number of physical disks and/or the segment size can improve performance. Figure 7: First Generation Firmware- Stripe distribution. File: stateCaptureData.txt Virtual Disk Unit 0 Configuration Volume Type: 13+1 RAID 5 User Label: MyRAID5_1 Block Size: 512 bytes Large IO: 4096 blocks Segment Size: 256 blocks Stripe Size: 3328 blocks ... IO Statistics: small small reads writes requests 2028332119 147699066 blocks 3091968111 2518067526 avg blocks 4 17 IO pct. 93.21% 6.78% large reads 0 0 0 0.00% large cache writes total hits 0 2176031185 1289775370 0 1315068341 4019884678 0 0 3 0.00% 0.00% 59.27% 1. IOs stripes /IO clusters /IO reads 2028332119 2034477363 1.00 2107869128 1.03 writes 147699066 148449472 1.00 157404718 1.06 2. write algorithms Full Partial RMW No Parity 1105611 12598366 32120072 0 RMW2 0 FSWT 0 December 2008 - Revision A01 Page 18