[Samba] Winbind process stuck at 100% after changing use_mmap to no

[Volker Lendecke]

On Tue, Jul 05, 2016 at 09:06:54PM +0100, Alex Crow wrote:
> >Why are you still using "use mmap = no" then?
> Because the wiki article does not explicitly state that mmap
> coherence is only needed for areas that store tdb files. I'd perhaps

Maybe that is the omission in the docs. I thought I had mentioned that
"use mmap" is only relevant for tdb files, not for plain exported
shares.

> incorrectly deduced that as you had explicitly said that "private
> dir" on the cluster FS was a bad idea, that disabling that would
> stop all tdb files being written to the MooseFS FS, and that would
> be the solution.

The solution is to use ctdb with the database files on local
directories. That's what ctdb is for.

> My understanding was the "use mmap" affected general FS operations
> from clients, not just tdb files.

It just affects tdb files.

> >This piece is wrong. The wiki should give you hints who wrote this.
> >Please contact the author of those lines, refer to the mail thread
> >here and ask these lines to be changed or even better -- change these
> >lines yourself.
> I see what you mean here, but I'd not want to edit a wiki when I
> have less idea of the facts that the person that wrote the original
> text! I'd not want to update it without knowing the precise facts,
> hence my reaching out to the Samba list and yourself.

Well, now you should have a better understanding of the issue :-)

> >If MooseFS does not even survive -rw without asking for mmap coherence,
> >just don't use it for Samba. This will eat your data for breakfast.
> >Gluster was there loooong ago, and they fixed it before becoming a
> >viable storage solution for Samba.
> >
> >Volker
> 
> MooseFS does not ask for mmap coherence. It has inconsistent results
> on a plain -rw test.

MooseFS needs to fix that. ping_pong with -rw is pretty basic Posix
stuff. Admittedly it seems to be very hard for cluster file systems to
implement, but it is essential if you want to provide Posix semantics.
Samba and SMB clients depend on this. SMB clients coordinate via byte
range locks, and data coherence coordinated by those locks just basically
assumed.

ping_pong was explicitly designed by Andrew Tridgell as a torture test
case for cluster file systems developers. It does not come with the
huge SMB baggage that is difficult to set up for cluster file systems
developers. The calls it makes are simple enough to be understandable
in file system traces.

Volker