XPWatch and XPSketch Reference guide for HP XP P9000 Performance Advisor

B Understanding write ratio in HP XP P9000Watch
The following screen shows the performance of the entire RAID group01-04 being collected with
the performance of LDEVs 01:6c, 01:6d, 02:a3, 02:a4, and 02:a5.
The LDEVs in RAID group 01-04 are exposed only throughx 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 01-04 shows some activity because it has another LDEV(01:f4) exposed through some
other ports (these LDEVs were not available for selection in HP XP P9000Watch 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))
= 100*(2/2)
= 100*1
= 100
The Wr% is 100% because all the front-end I/Os on that RAID group are writes.
NOTE: We can conclude all the front-end I/Os on the RAID group are writes because the r_H%
(cache read hit %) is 0; that is, there are no front-end reads.
68 Understanding write ratio in HP XP P9000Watch