[Linux-cluster] Samba failover "impossible" due to missing cifs client reconnect?

[Christopher R. Hertel]

On Wed, Sep 07, 2005 at 10:15:37PM +0200, Axel Thimm wrote:
> After having setup our workarounds for NFS we are very happy with how
> it's working. Now we're looking at Samba.
> 
> But we have quite a showstopper right at the beginning. The smb/cifs
> clients, be it smbclient or Windows XP, don't like their TCP stream
> being resetted and don't retry/reconnect (contrary to NFS).
>
> It looks like the protocol has no considerations for retries above the
> TCP/IP level. So when the TCP stream is torn on the server's side due
> to relocation (either due to crash/fencing or soft) any client
> smb/cifs activity is broken at that time.
>
> This means that any data transfer via smb/cifs shares during the
> relocation will fail, and there is nothing we can do on the server's
> side. Or is there?

Windows clients will reconnect to the same server, and so will smbfs and 
cifs-vfs.

I just tested this.  On a W/XP box I browsed through some directories on a 
share served by Samba.  I then shut Samba down, and tried viewing some 
different subdirectories of the same share.  Windows coughed up an error 
dialog.  I then restarted Samba and Windows got happy again.  I could 
browse through all of the subdirectories in the share.

We've talked about Samba on GFS within the Samba Team, and various members
have done some digging into the problem (Volker most recently, if I'm not
mistaken).  Samba must maintain a certain amount of state information
internally--including name mangling, locking, and sharing information
that--is peculiar to Windows+DOS+OS2 semantics.  The problem is ensuring 
that Samba's state information is also shared across the GFS nodes.

I've not had time to keep up with this development thread, but I know that 
the folks working on Samba-4 are aware of the issues involved.

Chris -)-----

-- 
"Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
Samba Team -- http://www.samba.org/     -)-----   Christopher R. Hertel
jCIFS Team -- http://jcifs.samba.org/   -)-----   ubiqx development, uninq.
ubiqx Team -- http://www.ubiqx.org/     -)-----   crh at ubiqx.mn.org
OnLineBook -- http://ubiqx.org/cifs/    -)-----   crh at ubiqx.org