[Linux-cluster] Starter Cluster / GFS

[Marti, Robert]

> -----Original Message-----
> From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-
> bounces at redhat.com] On Behalf Of Jankowski, Chris
> Sent: Wednesday, November 10, 2010 3:04 PM
> To: linux clustering
> Subject: Re: [Linux-cluster] Starter Cluster / GFS
> 
> Robert,
> 
> One reason is that with GFS2 you do not have to do fsck on the surviving
> node after one node in the cluster failed.
> 
> Doing fsck ona 20 TB filesystem with heaps of files may take well over an
> hour.
> 
> So, if you built your cluster for HA you'd rather avoid it.
> 
> The locks need to be recovered, but this is much faster operation and fairly
> time bound. Fsck is not.
> 
> Regards,
> 
> Chris Jankowski
> 
> -----Original Message-----
> From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-
> bounces at redhat.com] On Behalf Of Marti, Robert
> Sent: Thursday, 11 November 2010 07:51
> To: 'linux clustering'
> Subject: Re: [Linux-cluster] Starter Cluster / GFS
> 
> > -----Original Message-----
> > From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-
> > bounces at redhat.com] On Behalf Of Nicolas Ross
> > Sent: Wednesday, November 10, 2010 1:32 PM
> > To: linux clustering
> > Subject: Re: [Linux-cluster] Starter Cluster / GFS
> >
> > > We had to make similar changes to our application.
> > >
> > > Avoid allowing two (or more) hosts to create small files in the same
> > > shared directory within a GFS filesystem.  That particular case
> > > scales poorly with GFS.
> > >
> > > If you can partition things so that two hosts will never create
> > > files in the same directory (we used a per-host directory structure
> > > for our application), or perhaps direct all write operations to one
> > > host while other hosts only read from GFS, it should perform well.
> >
> > Ok, I see. Our applications will read/write into its own directory
> > most of the time. In the rare cases when it'll be possible that 2
> > nodes read/writes to the same directory, it'll be for php sessions
> > files. If we ever need to reach to this stage, we'll have to make a
> > custom session handler to put them into a central memcached or
> something else...
> >
> 
> If that's the case, why look at shared storage at all?
> 
> --

In this scenario, he's not building the apps for HA (single server at a time, except maybe for sessions) he's not using massive filesystems (5-6TB total)...

The overhead involved in managing shared storage isn't typically worth it if you're not going to leverage the shared portion of it.

Rob Marti