HP XP Performance Advisor Software - Manual (Page 57)

B Understanding write ratio in XPWatch
The following screen shows the performance of the entire RAID Group 01-03 being collected with the
performance of LDEVs 02:76, 02:77, and 02:78.
The LDEVs in RAID Group 01-03 are exposed only through port 1A. There are no I/O activities or
LDEVs reported on this port because there is no I/O activity in port 1A and these LDEVs are not visible
through any other port.
RAID Group 01-03 shows some activity because it has another LDEV(01:f4) exposed through some
other ports (these LDEVs were not available for selection in XPWatch as we selected only port 1A),
which have I/Os in it.
The average write percentage (Wr%) for the above output can be inferred by the following calculations:
Calculate the I/O per second:
I/O per second (total front-end writes + total front-end reads) = 2
r_H% (cache read hit %)=0 and Be (back-end I/O per second)=0
Because both of the above values are 0, it implies that there are no back-end reads or back-end writes
or front-end reads.
• Total front-end reads = 0
• Total front-end writes = 2
Therefore, Wr% can be calculated as:
Wr% = 100*(total front-end writes / (I/O per second))
XPWatch and XPSketch Reference Guide 57