-----Original Message----- From: Yong Huang [mailto:yong321@xxxxxxxxx] Sent: Friday, May 21, 2010 12:19 AM 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 > > ... Jack, You can look at the first iteration of your iostat output, which is the accumulative stats since bootup (the later iterations are each a 2-second sample). If your iostat had argument -p sdo instead of -p sdb (it must be a typo compared with the outpuf of your multipath command), you would see all four paths have almost perfectly equal I/O stats, because all your paths are active. Numbers below this accumulative stats indicate your currently selected paths are sdam and (likely) sdo (not shown due to typo). After rr_min_io seconds I think, they'll switch to the other two paths. Your multipath command seems to have the 4 path lines missing leading space; they should be indented below the priority group line. Is it OK you show me the first part of /etc/multipath.conf, uncommented lines before the actual multipaths section? BTW, I used a wrong word in my last message. Instead of "disk", I really should say "device". Yong Huang ========== Thanks for the follow up. You are correct I entered the wrong device name. I monitored again with the correct device names for an over all longer period of time and it did rotate through all the device. But it seemed to take about a few minutes to rotate from one path to the next. So I added rr_min_io 2 in the default section, ran multipathd -k, reconfigure, but it did not have any effect. I am reading the multipath.conf man page now to see if I can find out anything. You are correct there are 4 paths, in my original question I just used 2 as an example. Then you asked questions and I provided more information. And the lack of a space in the output of multipath -l is probably due to my copy and pasting. multipath.conf VVVVVVVVVVVVVV blacklist { devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*" devnode "^cciss!c[0-9]d[0-9]*" devnode "^hd[a-z]" devnode "^vg*" } ## Use user friendly names, instead of using WWIDs as names. defaults { user_friendly_names yes polling_interval 10 path_checker readsector0 path_selector "round-robin 0" path_grouping_policy multibus failback 5 no_path_retry 5 rr_min_io 2 bindings_file "/etc/multipath.bindings" } ^^^^^^^^^^^^^^^^^^ Everything else is commented out. It is using the build in multipath rule/configuration. device { vendor (HITACHI|HP) product OPEN-.* path_checker tur failback immediate no_path_retry 12 rr_min_io 1000 } Which when I was copy and pasting I noticed the rr_min_io 1000 which probably why it is taking a while to rotate through the paths. ----- Jack Allen -- redhat-list mailing list unsubscribe mailto:redhat-list-request@xxxxxxxxxx?subject=unsubscribe https://www.redhat.com/mailman/listinfo/redhat-list
