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Operating Systems Linux Red Hat Verify multipathing
# 1  
Old 10-01-2014
Verify multipathing

I have a couple of questions regarding multipath.

If I do vgdisplay vg01, I see it is using 1 PV: /dev/dm-13

If I type multipath -ll I see dm-9, dm-10, dm-11, dm-12, but do not see dm-13. Is my vg01 multipathed? How can I actually know for sure?

Secondly, let's say this time vg01 says it has one PV: /dev/sdab

I type multipath -ll and sure enough I see /dev/sdab but under mpath31. Is my vg01 multipathed even though I'm point my PV path to sdab instead of mpath31?

My expertise is in HP-UX and I haven't been doing Linux very long. Our resident Linux "experts" do not know the answers to these very important questions so I would appreciate any help or advice you can give.
# 2  
Old 10-01-2014
You should be using /dev/mapper/<mpath> device, which is created when you rescan the fabric and disk is available.

Also it is a good practice (but not neccesary) to define alias for your new disk with a meaningful name for that disk. You will have then /dev/mapper/<mpathalias> for using with pvcreate / vgcreate / vgextend etc. after you restart multipath daemon.

You might want to check the output of dmsetup ls and/or dmsetup info if your volume group(s) are using mpath or mpathalias devices.

If you used /dev/sd devices then there is a good chance multipath is not working for that disk, but i cannot say for sure.

Best is to test it on test machine using /dev/sd device (wrong way not per documentation) then removing one path physically.

Hope that helps
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