[mythtv-users] Network storage fault tolerance (was Re: Myth autoexpiring brand new shows)

Roger Heflin rogerheflin at gmail.com
Wed Aug 27 01:18:07 UTC 2008


Michael T. Dean wrote:
> On 08/26/2008 06:40 PM, David Brodbeck wrote:
>> Michael T. Dean wrote:
>>   
>>> Speaking of which, does anyone know of a way to make NFS tolerant of the 
>>> NFS server's going down so that it will automatically unmount/remount 
>>> the filesystems?
>>>     
>> Technically NFS is stateless -- if a server goes down, I/O requests on 
>> that filesystem just hang until it comes back.
> 
> For me the hanging part works, but the "until it comes back," doesn't 
> when there's a reboot of the server involved.  When the server comes 
> back, it continues to hang.  I have to unmount (which gives errors 
> because the server "isn't there"--even if it is).  Then, eventually, I 
> just remount, and it works (though sometimes it seems to show multiple 
> connections in the nfs *tab files).

How long do you wait?   The retry timeouts get larger until they get up
to a fairly large number of minutes (I don't remember what the max timeout is), 
so once the NFS server comes back it will take up to that time for things
to retry and continue one.

> 
>>   No need to remount. 
>> This usually isn't what people want, though, because it leads to lots of 
>> applications sitting around in unkillable D states.
> 
> I'm mounting with:
> 
> rw,_netdev,rsize=8192,wsize=8192,hard,intr,actimeo=0
> 
> (from http://mythtv.org/docs/mythtv-HOWTO-23.html#ss23.10 , but with 
> nfsvers=3 removed as it's not required on my systems).  But, after doing 
> some more reading on nfs.sf.net, I switched it to use nfs4 (rather than 
> 3) because it's supposed to be more reboot tolerant.  Can't test while 
> the backend is recording, but if it works, I'll try to remember to post 
> the results.

Lose the rsize/wsize too, you only really need it if your network is
screwed up, 8192 has not been an optimal setting for anything for quite
a while.

                         Roger
> 
> Mike
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