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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 redhat com [mailto:linux-cluster-bounces 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 redhat com [mailto:linux-cluster- 
> bounces 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?

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