GFS

Wed Oct 29 14:06:09 UTC 2008

Here's kind of the scenario I have in my head:  You have 10 machines you want to share /home.  These machines are otherwise unrelated and may be some mixture of DB, DNS, HTTP, LDAP, or whatever.  You could make a 10 node cluster without any applications or resources (basically just to handle the storage) and use GFS to mount up a shared LUN.  This would require every machine in that group to also run the various cluster services (fenced, aisexec, groupd, dlm_controld, clvmd, etc.) and should have each one set up with some sort of fencing mechanism.

Or, you could set up two little machines in a true failover cluster exporting /home from off the SAN via NFS to the 10 various machines.  Sure there'd be a bit of NFS overhead, but none of your other servers would have to worry about cluster stuff, like running all of that extra software or being fenced.

Whether or not this scenario is in anyway like what the original question asker had in mind, I don't know, but that's how I pictured it.

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Marti, Rob
Sent: Wednesday, October 29, 2008 8:51 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

My point was, you wanted to use a "small NFS cluster".  Theres no difference between a small NFS cluster, and using GFS directly.  Unless by cluster you didn't mean RHCS.

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Kristoffer Knigga
Sent: Wednesday, October 29, 2008 8:48 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

Well, because the cluster software would also cause overhead.  The cluster requires a half dozen or more extra services to be running.

Also, best practices require fencing to be set up and working.  I'd hate to have a machine with no failover capabilities spontaneously power cycled because of a network hiccup or something.  Though I suppose you could get around that with fiber switch fencing instead of power fencing, but still, it wouldn't be pretty.

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Marti, Rob
Sent: Wednesday, October 29, 2008 8:38 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

Depends... since you still have to have shared storage, and more than likely GFS, why add the overhead of NFS?

Rob

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Kristoffer Knigga
Sent: Wednesday, October 29, 2008 8:35 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

For something like /home, though, an small NFS cluster would probably be way less of a hassle than a huge cluster and it would still eliminate the single point of failure.

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Marti, Rob
Sent: Wednesday, October 29, 2008 8:26 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

Its at least a partial replacement - instead of a single box exporting an NFS share for a bunch of boxes to mount (IE single point of failure) you have each box mount it directly.

But yes, you need the clusterware installed and configured for gfs to be useable.

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Kristoffer Knigga
Sent: Wednesday, October 29, 2008 8:24 AM
To: General Red Hat Linux discussion list
Subject: RE: GFS

I just took RH436 last week, so here is what I understand from that:

You must have a basic cluster set up to use GFS.  The reason being that everything using a shared file system like this must be able to communicate in order to negotiate locking.  If there was no such communication, you'd have the possibility of node1 and node2 trying to write the same block at the same time, and thus causing inconsistent data.  Red Hat Cluster Suite manages this communication to ensure everything is copasetic.

Shared storage + GFS is not a replacement for NFS.

Kris

-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Ryan Golhar
Sent: Tuesday, October 07, 2008 3:50 PM
To: General Red Hat Linux discussion list
Subject: GFS

Has anyone successfully setup GFS?  I have SAN connected to several
computers by fibre, and it appears that GFS is the way to go as opposed
to use an NFS server.

Do I really need to set up all the other aspects of a Redhat cluster to
get GFS to work?  There doesn't seem to be a good HOW-TO of this
anywhere, and the RedHat docs are not as helpful as I would have liked.

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