[Linux-cluster] GFS is for what and how it works ?

[Halomoan Chow]

Thank you Bowie
You gave me a little light in GFS jungle :D


Regards,

Halomoan


-----Original Message-----
From: Bowie Bailey [mailto:Bowie_Bailey at BUC.com] 
Sent: Monday, April 03, 2006 10:31 PM
To: halomoan at powere2e.com
Cc: linux clustering
Subject: RE: [Linux-cluster] GFS is for what and how it works ?

Halomoan wrote:
> Sorry, I'm newbie in GFS.
> 
> Followed Redhat's GFS documentation
> To find out how GFS works, I have 2 nodes (node A and node B) for
> GFS and 1 node (node C) for GNBD server. It runs with no error but i
> don't know how to use it (GFS)  
> 
> I attached my /etc/cluster/cluster.conf below.
> 
> My question is:
> 
> 1. At a time, how many nodes have GFS filesystem mounted ? Where is
> the cluster's work in GFS ? 

You can mount one node for each journal you created when you built the
GFS filesystem.

What the cluster does is manage access to the GFS filesystem and
(attempt to) ensure that if one node starts having problems, it can't
corrupt the filesystem.

> 2. How do I shared the GFS filesystem to other server ? Do I need
> other software ? 

GFS is simply a filesystem which is capable of being used on multiple
nodes at the same time.  How you mount it depends on what software or
hardware you are using to share the media.  GNBD can be used by a
server to share it's storage with the other nodes.  You can also use
iSCSI, aoe, and others to connect each node directly to a separate
storage unit.

> 3. From this configuration, if node A failed, what happen to the GFS
> filesystem ? failover to node B ? How about with the other server
> that is using the GFS filesystem in node A ?  

There is no failover.  Everything is always active.  As long as the
storage itself doesn't fail, the failure of one node should not be a
problem.  Unless, of course, it causes your cluster to lose quorum
(drop below the minimum number of servers necessary to maintain the
cluster).

> 4. Could you give me example what is actually the GFS real usage in
> real live ? 

I'm using it to share a 1.2 TB storage area between two systems that
use it for processing and a third system that has direct access for
making backups.

> I'm absolutely confuse with this GFS on how they works.

Yea.  The documentation is not very extensive at this point.

-- 
Bowie