RE: Multipath I/O stats

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-----Original Message-----
From: Yong Huang [mailto:yong321@xxxxxxxxx] 
Sent: Thursday, May 20, 2010 2:28 PM
To: Allen, Jack
Cc: redhat-list@xxxxxxxxxx
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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