Multipath I/O stats
Allen, Jack
Jack.Allen at mckesson.com
Thu May 20 20:33:45 UTC 2010
-----Original Message-----
From: Yong Huang [mailto:yong321 at yahoo.com]
Sent: Thursday, May 20, 2010 2:28 PM
To: Allen, Jack
Cc: redhat-list at redhat.com
Subject: Re: Multipath I/O stats
> With multipath set up to access a SAN with some number of LUNs
> and for this question 2 paths set for round robin, how can the
> I/O stats be seen/gathered to see the throughput on each path
> and how balanced the I/O is?
I think we can do this. multiptha -l tells you what disks are combined
to form a mapper path. Then you can use iostat to check I/O stats of
each disk along with each mapper. It won't be hard to write a shell
script to re-print the lines of iostat nicely, grouping the lines of the
disks under their respective mapper path.
Yong Huang
===========================
Thanks for the reply.
This is the output of just one of the mpaths that I monitored for a
while.
mpath13 (360060e8005491000000049100000703c) dm-0 HP,OPEN-V
[size=10G][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=0][active]
\_ 2:0:0:2 sdaa 65:160 [active][undef]
\_ 2:0:1:2 sdam 66:96 [active][undef]
\_ 1:0:0:2 sdc 8:32 [active][undef]
\_ 1:0:1:2 sdo 8:224 [active][undef]
Below is the command I used and the results. I know this is a small
sampling and I have eliminated the ones that had 0 I/O to save space
here. But it appears the I/O is not really being done round-robin as I
think it should be. You will notice sdam and sdb are the only ones that
do any I/O. Now maybe this is because of some preferred path and
controller relationship, I don't know. Any help understanding this would
be helpful.
iostat -d -p sdaa -p sdam -p sdc -p sdb -p dm-0 2 20 > /tmp/zzxx
Linux 2.6.18-164.el5PAE (h0009) 05/20/2010
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 1.53 49.43 15.03 60932848 18523880
sdam 1.53 49.35 15.10 60833016 18616608
sdc 1.53 49.41 15.04 60905568 18542936
sdb 1.38 57.21 3.68 70522704 4533144
dm-0 32.23 197.56 60.24 243542080 74259264
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 4.50 72.00 0.00 144 0
sdc 0.00 0.00 0.00 0 0
sdb 4.50 72.00 0.00 144 0
dm-0 9.00 72.00 0.00 144 0
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 10.00 160.00 0.00 320 0
sdc 0.00 0.00 0.00 0 0
sdb 7.50 112.00 8.00 224 16
dm-0 20.00 160.00 0.00 320 0
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 7.00 112.00 0.00 224 0
sdc 0.00 0.00 0.00 0 0
sdb 5.00 80.00 0.00 160 0
dm-0 14.00 112.00 0.00 224 0
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 3.50 56.00 0.00 112 0
sdc 0.00 0.00 0.00 0 0
sdb 3.50 56.00 0.00 112 0
dm-0 7.00 56.00 0.00 112 0
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 0.50 0.00 7.96 0 16
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 1.00 0.00 7.96 0 16
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 3.50 32.00 96.00 64 192
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 16.00 32.00 96.00 64 192
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 0.50 0.00 8.00 0 16
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 1.00 0.00 8.00 0 16
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 1.50 0.00 24.00 0 48
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 3.00 0.00 24.00 0 48
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 5.00 24.00 88.00 48 176
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 14.00 24.00 88.00 48 176
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 0.50 8.00 0.00 16 0
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 1.00 8.00 0.00 16 0
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sdaa 0.00 0.00 0.00 0 0
sdam 7.50 0.00 120.00 0 240
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
dm-0 15.00 0.00 120.00 0 240
-----
Jack Allen
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