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Old 01-17-2016, 03:11 AM   #1
JoeW
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Intermittent high IO wait stalling server - suspect cifs mount


Hi, I have a raspbian installation running a media server (subsonic) which is reading from a remote smb share which is mounted locally, with this in fstab:
//192.168.0.12/media /media/usbhdd1 cifs guest,uid=1000,gid=1000,iocharset=utf8 0 0

This all works fine 95% if the time, but then I'll get times when the whole system stalls, and CPU iowait shows 98-100% for up to a minute.

There's nothing else running on this system, and disk not busy, so fairly sure the iowait is network, which will be the cifs mount.

Has anyone seen this? How to diagnose/fix ? I've started looking at cifs mount options - rsize, caching, but am just guessing.
 
Old 01-18-2016, 08:19 AM   #2
dijetlo
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Hi Joe,

Are the media server and the CIFS host on an isolated network? Is it a wireless or cabled medium?
Are their any other clients for the CIFS host and if so, are they experiencing the same issues?
Can you reproduce the issue ? Does it occur at regular intervals? Occur when a particular type of media (or perhaps even a particular file) is being served?
Have you checked dmesg on the CIFS host for debugging information?
Have you changed the log level on the CIFS host to capture extended diagnostics during any of these events?

Our friends at SAMBA have given us some general direction regarding troubleshooting you might find helpful.

In answer to your question, I've run into something similar before however it was being caused by network saturation corresponding to an overly pre-emptive back-up operation (though I've heard file system corruption can give you the same issue).
 
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Old 01-18-2016, 03:32 PM   #3
JoeW
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Hi, thanks for the detailed reply. This is my home network, and the two linux hosts with the problem are cabled. There are also wired and wireless windows clients of the cifs/samba share which do not seem to have the problem. There are no other linux boxes as cifs client. It happens at apparently fairly random intervals - sometimes twice in 10 minutes, and then not again for an hour. All I'm doing is streaming mp3 files. The same file does not cause problems in the same place, so not reproducible.

I hadn't seen that cifs troubleshooting info - thanks, I'll need to spend some time giving it a go. So far, I've tried reducing rsize from its default of 1M to 100K, and that seems to have helped - I haven't seen a hang since doing that. It's been suggested elsewhere that I should drop cifs altogether for linux->linux, and run an nfs server for that. Seems overkill to run nfs and cifs at same time though (I have windows clients that need to attach too).

cheers
 
Old 01-18-2016, 04:40 PM   #4
suicidaleggroll
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Quote:
Originally Posted by JoeW View Post
Seems overkill to run nfs and cifs at same time though (I have windows clients that need to attach too).
I don't think so at all. NFS overhead is significantly lower and the connection should be far more reliable. There's nothing wrong with sharing a directory using two different network protocols, let the clients connect as they see fit.
 
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Old 01-18-2016, 05:18 PM   #5
JoeW
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Thanks, I think I'll go with nfs then, rather than struggling with cifs.
 
  


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