[mythtv-users] Fine-tuning NFS parameters

Kevin Ross kevin at familyross.net
Sat Jul 24 01:17:18 UTC 2010


On 07/23/2010 05:15 PM, Gavin Hurlbut wrote:
>
>     intr: deprecated
>
>
>
> Not deprecated in my man page.
>

"The intr / nointr mount option is deprecated after kernel 2.6.25.  Only 
SIGKILL can interrupt a pending NFS operation on these kernels, and if 
specified, this mount option is ignored to provide backwards 
compatibility with older kernels."

Maybe you're using an older distro, like Debian Stable or something.  Or 
something non-Linux, like Solaris or BSD.

>     rsize/wsize: The "TRANSPORT METHODS" section of the man page says
>     you should specify rsize and wsize when using UDP, not when using
>     TCP.  And all modern NFS implementations use TCP.
>
>     nfsvers: autonegotiated to 3 if both sides support it, otherwise
>     2.  So this seems unnecessary also.
>
>
> If your NFS server doesn't require the options, great.  However...  If 
> it does NOT, you should do it...
>
> nfsvers=3 is a minimum.  If both sides do not support 3, you want the 
> mount to FAIL.  NFSv2 does not support files > 2GB in size, making it 
> absolutely useless for mythtv recordings.
>

Okay, sounds good to me. :)

> As for the rsize/wsize...  I don't care what your man page indicates, 
> those are the parameters to tweak for performance in NFS.  If your 
> setup defaults to good settings, great.  I would not presume that "all 
> modern...." means squat.  I have seen "modern" NFS implementations 
> that use UDP, and that require the options stated.
>
> The *default* rsize/wsize for many NFS servers is 4k.  This sucks 
> really badly for performance, especially on GigE.

My NFS server *does* give good defaults.  Here is what I get mounting 
with just the "rw" option, and exported with "rw,async":

  Flags: rw, relatime, vers=3, rsize=262144, wsize=262144, namlen=255, 
hard, proto=tcp, timeo=600, retrans=2, sec=sys, mountaddr=192.168.1.2, 
mountvers=3, mountport=37760, mountproto=udp, addr=192.168.1.2

I don't have as much experience with NFS as you obviously do.  I'm only 
going by my man page and the results I see on my system.  I believe all 
modern Linux distros will see similar results, since they all use the 
same NFS implementation, namely the one built into the Linux kernel.  
Obviously Solaris, BSD, old userspace Linux NFS, etc. may be implemented 
differently.

It's Friday, and I've been in front of a computer long enough for 
today.  Have a good weekend!

-- Kevin

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