[mythtv-users] mythtv + nfs = bad?

Alex Pearson alex at apics.co.uk
Sat May 9 10:41:55 UTC 2009


Hi All,
        I'm not sure if this will help anyone, but I found nfs unstable on 
my box at home (which runs a number of nfs root'd servers as well as 
mythtv storage), I resolved the issue by setting the clients to tcp and 
also increasing the block size.  I now use the following mount options:
                defaults,tcp,rsize=8192,wsize=8192 for general servers.
                defaults,tcp,rsize=8192,wsize=8192,actimeo=0 for mythtv.

        I should point out I found the above 'fix' was born out of a bit 
of guess work and assumption around what was causing my issues.  I'm also 
running 16 nfsd's (although I don't recall this was required to fix my 
stability issues)

Hope this helps (disregard if a load of rubbish!)

Alex



mythtv-users-bounces at mythtv.org wrote on 09/05/2009 05:59:57:

> From:
> 
> Nasa <nasa01 at comcast.net>
> 
> To:
> 
> Discussion about mythtv <mythtv-users at mythtv.org>
> 
> Date:
> 
> 09/05/2009 05:06
> 
> Subject:
> 
> Re: [mythtv-users] mythtv + nfs = bad?
> 
> Sent by:
> 
> mythtv-users-bounces at mythtv.org
> 
> 
> ----- "Dale Pontius" <DEPontius at edgehp.net> wrote:
> 
> > Brian Wood wrote:
> > > On Thursday 07 May 2009 07:43:38 James Oltman wrote:
> > >> On Wed, May 6, 2009 at 6:55 PM, Brian Wood <beww at beww.org> wrote:
> > >>> What version of NFS?
> > >>>
> > >>> I think NFS v.2 (client side) has a 2GB file size limit, which
> > means it
> > >>> can only look at the first 2GB of a file that's larger than 2GB.
> > >>>
> > >>> Version 3 supports larger files, but obviously it depends on the
> > >>> filesystem on
> > >>> the server side, if it were FAT, for example, a 4.7GB file would
> > be a
> > >>> problem.
> > >>>
> > >>> There is also a limit on the size of a transfer "on the wire",
> > which
> > >>> depends
> > >>> on whether TCP or UDP is used, and the particular implementation.
> > >>>
> > >>> Large files and NFS can be problematical, make sure you understand
> > any
> > >>> limits
> > >>> of your server and client NFS versions, as well as the filesystem
> > in use.
> > >>>
> > >>> Google "nfs file size limits" for more information.
> > >> Brian,
> > >>
> > >> Thanks for the response.  What was strange about my setup was that
> > it was
> > >> working just fine for a long time.  Then all of the sudden, one
> > day, it
> > >> stopped working.  I don't know if it happened during a kernel
> > update or
> > >> what.  I know I'm running NFSv2.  I don't know how to update myself
> > to v3
> > >> or above.
> > > 
> > > 
> > > The precise upgrade method would depend on your distribution, any of
> > the most 
> > > recent distros should have support for v3. I'd consult the relevant
> > support 
> > > fori.
> > > 
> > > Even if (for example) an upgrade to your server side machine enabled
> > nfs v3, 
> > > the systems should negotiate the highest commonly supported version,
> > so if 
> > > your client can only do v2, that's what the server should do as
> > well.
> > > 
> > > There have also been some changes in the default settings for
> > sync/async, and 
> > > some others I think.
> > > 
> > > But using "mixed" systems might cause problems.
> > > 
> > > Another user here noted an improvement in performance by using samba
> > mounts 
> > > instead of NFS, certainly sounds like it's worth a try. I'm going to
> > look 
> > > into that, and try to get some hard numbers.
> > > 
> > > I'm certainly no expert on NFS, I use it for non-Myth applications
> > and it has 
> > > always "just worked", but I don't put much demand on it. 
> > > 
> > I'm running nfs4 and still have the problems.  It's supposed to be 
> > ironed out by the time client and server get to 2.6.29 or beyond.
> > 
> This discussion got me to do some googling....  I came across some 
> discussion, such as here:
> 
> http://www.ncsa.uiuc.edu/UserInfo/Resources/Hardware/IBMp690/IBM/
> usr/share/man/info/en_US/a_doc_lib/aixbman/prftungd/2365ca3.htm
> 
> which eventually led me to see this...
> 
> http://kamilkisiel.blogspot.com/2007/11/understanding-linux-nfsd-
> statistics.html
> 
> Those combined with some more research led me to believe I wasn't 
> running enough nfsd daemons.  The default of 8 just isn't good 
> enough -- does that account for the
> problem I was seeing, I guess time will tell.  But it's at least a 
start.
> 
> Nasa
> 
> 
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