> On Jul 28, 2016, at 9:54 PM, sohamm <soh...@gmail.com> wrote:
> 
> Client is configured for IB interface. 

So it looks like there might be something wrong with the LNet config on the 
client then.  Based on the output from “lctl ping” that you ran from the 
server, the client only reported a NID on the tcp network.

> in my understanding i can specific the network of choice in the mount 
> command. tried both tcp and ib.

That is true, but sometimes if the client and server both have interfaces on 
two different networks (like ethernet and IB) there can be some subtle issues.  
When you specify the NID for the MGS to mount the file system, the client will 
retrieve information about the MDS/OSS servers from the MGS you specified.  
This information includes the NIDS that the MDS/OSS servers will listen for 
requests.  If a client sees that a server has a NID on tcp0 and a NID on o2ib0, 
and the client also has NIDs on tcp0 and o2ib0, then the client sees that there 
are two paths to the same server and it will just pick one of the paths (which 
might not be the one you want).  And if the path it chooses happens to be down, 
it won’t matter if the other path is up.

(Now, I should make a disclaimer about the above statements.  I believe that is 
how it worked on Lustre versions like 1.8 and 2.4.  I have not tried this with 
newer Lustre versions, so the behavior could be different.  I also have not 
experimented with anything like specifying weights for LNet routes, so I don’t 
know if that could be used to prefer one interface over another.)

--
Rick Mohr
Senior HPC System Administrator
National Institute for Computational Sciences
http://www.nics.tennessee.edu

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