[Linux-cluster] Starter Cluster / GFS

Gordan Bobic gordan at bobich.net
Wed Nov 10 08:13:21 UTC 2010

Nicolas Ross wrote:

> So today I dug up on Gfs2 on Redhat's site and it petty much fits my 
> need. It seems to be a very powerfull solution. If I understand 
> correctly, I need to setup a cluster of nodes to use Gfs. Fine with 
> that. But since it's not a real "cluster", do I stil need the quorum to 
> operate the global file system ? On our setup, a particular service runs 
> on a single node from the shared filesystem.

If you want the FS mounted on all nodes at the same time then all those 
nodes must be a part of the cluster, and they have to be quorate 
(majority of nodes have to be up). You don't need a quorum block device, 
but it can be useful when you have only 2 nodes.

If you are only ever going to have the SAN volume mounted on one device 
at a time, don't bother with GFS and make the SAN block device a 
fail-over resource so that only one node can mount it at a time, and put 
a normal non-shared FS on it. You will get better performance.

> The documentation on redhat's site is very technichal, but lacks some 
> beginer's hints. For instance, there's a part about the required number 
> of journal to create and the size of those. But I cannot find suggested 
> size or any thumb-rule for those...

The number of journals needs to be equal to or greater than the number 
of nodes you have in a cluster. e.g. if you have 5 nodes in a cluster, 
you need at least 5 journals. If you think you might upgrade your 
cluster to 10 nodes at some point in the future, then create 10 
journals, as this needs to be done at FS creation time.


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