Re: Raspberry Pi 2, nfs mount hangs after some time

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Mon, 26 Oct 2015 19:39:23 +0700
    From:        Pongthep Kulkrisada <ptkrisada%gmail.com@localhost>
    Message-ID:  <20151026123923.GA34%gmail.com@localhost>

  | Please you be specific or kindly give some examples.

It has been a long time, but if you search the list archives you'll
find many references to hangs using NFS.   I recall no actual fixes
(plenty of avoidance suggestions.)

Almost for sure the trigger is lost packets, perhaps only in some specific
situations, rather than just any lost packets, which is why tcp helps,
it will usually recover fine, and all NFS sees is a slight delay.

That would mean that if (in practice) your net loses very few packets, you
might never experience a problem.

But try swamping the net &/or server (mbufs in particular) while attempting
a UDP mounted busy NFS connection (ie: force lost packets) and I expect
you'll see the problem too.

When we were doing this we had dozens of busy nfs clients (or as busy
as SS1's and 486 class PCs of the vintage can ever be) sharing a 10Mbps
(thin wire) ethernet - lost packets would have been common.   Hangs were
not exactly frequent, even there, but often enough to be noticeable.

kre