Write Algorithm Data - Dell PowerVault MD3000i Tuning Manual

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices
Figure 8: Second Generation Firmware– Stripe distribution. File:
Volume 0 Attributes:
Volume Type:
User Label:
...
BlockSize:
LargeIoSize:
...
Perf. Stats:
1.
...
*** Performance stats ***
Cluster Reads
Stripe Writes
RPA Requests
Full Writes
2.
No Parity Writes

4.7.5 Write Algorithm Data

It is important to understand the effect determining the most suitable RAID level
can be a daunting task. Understanding the effect of which write algorithm is in
use is an important part of RAID Level balance. The possible choices in first
generation firmware, as seen in Figure 9, are Full, Partial, RMW, RMW2, and the
Full Stripe Write-Through. RMW2 was folded into RMW statistics in the second
generation firmware (see Figure 10).
The Full algorithm takes an entire stripe of data and dumps it to the disk,
depending on the RAID level of choice, P or P and Q will get calculated at this
point. This is the most efficient type of write that can be performed, and the
design of a disk group should be around maximizing full writes.
Partial writes are when less than a full stripe of data non-aligned with segment
boundaries are modified and written. In RAID level 5 and 6 this is more complex,
as parity data must be recalculated for the whole stripe. Partial writes are a
worst-case algorithm and should be minimized. Larger quantities of partial writes
than full writes can indicate use of an inappropriate segment size.
December 2008 – Revision A01
stateCaptureData.txt
RAIDVolume
MyRAID10_One
512 bytes
4096 blocks
Requests
Reads 67456452 5943724625
Writes 27283249 1144902648
Large Reads
Large Writes
Total 94739701 7088627273
Cluster Writes
6252626 3015009
Cache Hits
2040493 4685032
RPA Width
982036 3932113
Partial Writes
653386
Fast Writes
0
3.
Blocks Avg. Blks
0 0
0 0
Stripe Reads
5334257
Cache Hit Blks
737770040
RPA Depth
418860162
RMW Writes
29 328612
Full Stripe WT
0
IO Percent
88 71.20%
41 28.80%
0 0.00%
0 0.00%
74 100.33%
2.
0
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