Re: Problem with Samba re-share of a CIFS mount

[Gionatan Danti <g.danti-N44kj/XGErOonA0d6jMUrA@public.gmane.org>]

On 02/13/2014 12:37 PM, Jeff Layton wrote:
>
> Using cache=none sort of defeats the purpose. After all Gionatan said
> that he was doing this specifically to use fscache, and that won't work
> with cache=none.
>

Surely my idea was to use FSCACHE to speed up remote access. Without it, 
the entire discussion is pointless...

> But, lets leave that aside for a moment and consider whether this could
> work at all. Assume we have samba set up re-share a cifs mount:
>
> Client sends an open to samba and requests an oplock. Samba then opens
> a file on the cifs mount, and does not request an oplock (because of
> cache=none). We then attempt to set a lease, which will fail because we
> don't have an oplock. Now you're no better off (and probably worse off)
> since you have zero caching going on and are having to bounce each
> request through an extra hop.
>
> So, suppose you disable "kernel oplocks" in samba in order to get samba
> to hand out L2 oplocks in this situation. Another client then comes
> along on the main (primary) server and changes a file. Samba is then
> not aware of that change and hilarity (aka data corruption) ensues.
>

Are you of the same advice for low-frequency file changes (eg: office 
files)?

What about using NFS to export the Fileserver directory, mount it (via 
mount.nfs) on the remote Linux box and then sharing via Samba? It is a 
horrible frankenstein?

> I just don't see how re-sharing a cifs mount is a good idea, unless you
> are absolutely certain that the data you're resharing won't ever
> change. If that's the case, then you're almost certainly better off
> keeping a local copy on the samba server and sharing that out.
>

After many tests, I tend to agree. Using a Fedora 20 test machine with 
fscache+cachefilesd as the remote Linux box, I had one kernel panic and 
multiple failed file copies (with Windows complaing about a "bad 
signature").

I also found this: https://bugzilla.redhat.com/show_bug.cgi?id=646224
Maybe the CIFS FSCACHE is not really production-grade on latest distros 
also?

Thank you and regards.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
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