Dell PowerVault MD3000i - Manual (Page 18)

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices
December 2008 – Revision A01 Page 18
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.
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 large large cache
reads writes reads writes total hits
requests 2028332119 147699066 0 0 2176031185 1289775370
blocks 3091968111 2518067526 0 0 1315068341 4019884678
avg blocks 4 17 0 0 0 3
IO pct. 93.21% 6.78% 0.00% 0.00% 0.00% 59.27%
IOs stripes /IO clusters /IO
reads 2028332119 2034477363 1.00 2107869128 1.03
writes 147699066 148449472 1.00 157404718 1.06
write Full Partial RMW No Parity RMW2 FSWT
algorithms 1105611 12598366 32120072 0 0 0
Figure 7: First Generation Firmware– Stripe distribution. File: stateCaptureData.txt
1.
2.