[Samba] gpfs + sernet samba + ctdb + transparent failover confusion

[Michael Adam]

Hi Sabuj,

SMB transparent failover is a new feature of SMB version 3.0
that is (cum grano salis) also known as Continuously Available
shares or persistent file handles.

This is a feature that is not yet implemented in Samba.
We are working on it, but there is a way to go...

Trigde's movies created the impression of a transparent
fail over, but this is in fact not the case: in those
demos, tride copied very small files in loop. After a
node failure, the client simply reconnected to a different
node (same IP), and potentially repeated the lost copy.
There were no long-running I/O ops involved.

The concept of durable file handles (from SMB2) can
provide transparent failover without interruption of I/O
in some cases. Durable file handles are implemented
starting with Samba 4.0. (See the manual page smb.conf
how to activate them.)

You won't get transparent fail over though if you kill
smbd or the node, though. If you do "ctdb disable" on
the active node though, you will see the I/O continuing
on the other node!

Cheers - Michael

On 2014-01-23 at 16:19 -0600, Sabuj Pattanayek wrote:
> Hi all,
> 
> We're running gpfs 3.5.0.12 (5 total nsds & quorum servers, 2 nsds running
> samba), sernet-samba 4.1.4-7, and ctdb 1.0.114.7-1 and trying to get
> transparent failover to work from a windows 8 client. We have ctdb failover
> working, i.e. if I run mmshutdown on one of the nodes the IPs failover in a
> few seconds after the GPFS mount is unmounted. For our transparent failover
> test, I open up firefox and start downloading a large file, e.g. a centos
> 6.5 iso into the mapped network drive being served up by one of the samba
> servers. Then I run an "mmshutdown" on the samba server the client is
> connected to and as soon as the mount disappears on the server the download
> stops and firefox throws an error. I was expecting that with transparent
> failover that the download would "hang" until the IPs had a chance to
> failover and the download/writes would continue but that didn't seem to
> happen.
> 
> Any idea on how to get this to work? Do we need to use ctdb 2.5.1? What's
> the difference between the sernet-samba provided ctdb 1.0.114 and the ctdb
> 2.5.1 line ? I tried to install the samba.org provided ctdb 2.5.1 RPMs but
> it failed with :
> 
> ctdb >= 1.0.115 conflicts with sernet-samba-4.1.4-7.el6.x86_64
> 
> I also created rpm's using the spec file from the ctdb-2.5.1 sources and
> got the same error. Looks like using "make install" would be the only way
> to get this installed, but even then why is sernet-samba requireing the
> 1.0.x line? Again, does it even matter with the original issue with
> transparent failover?
> 
> Thanks,
> Sabuj
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