[mdlug] Samba and F5 for Failover?

[Robert Adkins]

> -----Original Message-----
> From: mdlug-bounces at mdlug.org 
> [mailto:mdlug-bounces at mdlug.org] On Behalf Of Adam Tauno Williams
> Sent: Wednesday, October 07, 2009 10:29 AM
> To: MDLUG's Main discussion list
> Subject: Re: [mdlug] Samba and F5 for Failover?
> 
> On Wed, 2009-10-07 at 10:18 -0400, Wojtak, Greg wrote:
> > Thanks Rob.  I think this gives me all I need.  I am failing across 
> > datacenters in different cities.  The requirement is for a DR 
> > situation, so *immediate* failover is not a requirement.
> 
> Ok, if the clients reboot you should be OK.
> 

  Wrong. The clients will not need to reboot.

  I have been running Samba as our primary domain controller for going on 8
years now. If the Samba server goes down, which has happened for various
sundry reasons over the past 8 years, bringing the server back up will allow
the clients to reconnect.

  The only problems we end up with is for very certain applications that
utilize pseudo database functions, like Quickbooks.

  Our CAD/CAM systems do not hiccup when they are using a file over the
network that is lost due to the server crapping out, just the Database
styled apps.

> > Our samba servers are on our SAN and the disk is being 
> replicated from 
> > one to the other.
> 
> Make sure you are replicating snapshots and not just the live image.
> That way you can go back to retrieve good copies of the 
> [inevitable] trashed files.
> 

  I would suggest doing this as well. Except I have never seen files become
trashed.

> > So it sounds like I can just keep the configs in sync 
> (maybe put all 
> > the required configuration info on a small replicated volume?) and 
> > when our primary datacenter gets exploded (ha!) I can just 
> fire up the 
> > "DR" samba server and set the F5 to send requests to that server.
> 
> Until the CIFS clients reestablish state with the new file 
> server they will see scads of errors.
> 

  If the underlying files are the exact same files that were connected to a
few minutes previously, by the other Samba server. There should be no
issues, except for with certain database styled applications, like
Quickbooks.

  My suggestion is to keep the files to be shared on a separate device that
is mounted by both Samba servers and then shared by both Samba servers. This
way any oplocks/what-not, will remain the same, the only difference being...
Well not much of anything.

  Part of the protocol for Server B taking over Server A's job should be to
activate a secondary ethernet card or replace it's current IP Addressing
with that of Server A's address, in order to preserve NetBIOS names and the
Primary WINS Server addressing.

  This should work perfectly fine, since using the exact same configuration
files on both servers will appear to be no different to the workstations, as
the SIDS will be the same. I love this about Samba as it has allowed me to
shift the entire domain from one server to another a good half a dozen times
without me having to run around and manually reboot or rejoin workstations
to the "new" domain server. (Of course, I don't perform such changeovers
during normal business hours, unless I am in a bind.)

  I wouldn't call myself some sort of uber genius with Samba. What I have
learned through years of working with Samba is that it is incredibly robust
and very easy to "play with" as described above.

	-Rob