[lustre-discuss] "Not on preferred path" error

Ben Evans bevans at cray.com
Tue Sep 20 11:48:49 PDT 2016

multipath is a linux utility which handles communications from the server
to the disk array.  It is independent of Lustre or Infiniband.  For OSSes,
each OSS had 2 connections to each storage array it communicated with,
usually there were a pair of arrays per OSS pair (except for in a rare
handful of our systems which had 1).

-Ben Evans

On 9/20/16, 2:33 PM, "lustre-discuss on behalf of Lewis Hyatt"
<lustre-discuss-bounces at lists.lustre.org on behalf of lhyatt at gmail.com>

>Thanks so much for the information, we will look into this asap.
>Forgive my ignorance, but is multipath here referring to some
>or infiniband-related process? Not familiar with it in this context.
>Thanks again.
>On 9/20/16 2:24 PM, Ben Evans wrote:
>> Lewis,
>> Yes, "Not on preferred path" is something that bubbles up through the TS
>> gui from multipath.
>> A simple thing you can check is running multipath -ll on the OSS (and
>> peer) in question and seeing if it reports that one or more path is
>> If it's just on one OSS, try running 'multipath -r'.  If it doesn't come
>> back and look OK, then it's most likely a cable issue, and you can try
>> re-seating it to see if it helps.  It's been a long time since I
>> this, though and can't remember the details of how to associate cables
>> with paths, though there should be indicator lights on the back of
>> everything and the path that is down should be red.
>> The high load is probably associated with the cable issue, since you're
>> putting more strain on one path.
>> -Ben Evans
>> On 9/20/16, 12:21 PM, "lustre-discuss on behalf of Lewis Hyatt"
>> <lustre-discuss-bounces at lists.lustre.org on behalf of lhyatt at gmail.com>
>> wrote:
>>> Hello-
>>> I am having an issue with a lustre 1.8 array that I have little hope
>>> of figuring out on my own, so I thought I would try here to see if
>>> anyone might know what this warning/error means. Our array was built
>>> by Terascala, which no longer exists, so we have no support for it and
>>> little documentation (and not much in-house knowledge). I see this
>>> complaint "Not on preferred path" on the GUI that we have, which I
>>> assume was something custom made by Terascala, and I am not sure even
>>> what path it is referring to; we use infiniband for all connections
>>> and it could relate to this, but not sure. We see this error on 3 of
>>> the 12 OSTs. More specifically, we have 2 OSSs, each handling 6 OSTs,
>>> and all 3 of the "not on optimal path" OSTs are on the same OSS.
>>> We do not know if it's related, but this same OSS is in a very bad
>>> state, with very high load average (200), very high I/O wait time, and
>>> taking many seconds to respond to each read request, making the array
>>> more or less unusable. That's the problem we are trying to fix.
>>> I realize there's not much hope for anyone to help us with that given
>>> how little information I am able to provide. But I was hoping someone
>>> out there might know what this "not on optimal path" error means, and
>>> if it matters for anything or not, so we have somewhere to start.
>>> Thanks very much!
>>> I could provide screen shots of the management GUI we have, if it
>>> would be informative.
>>> -Lewis
>>> _______________________________________________
>>> lustre-discuss mailing list
>>> lustre-discuss at lists.lustre.org
>>> http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
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