[ClusterLabs] principal questions to a two-node cluster

Michael Schwartzkopff ms at sys4.de
Mon Apr 20 09:36:49 EDT 2015

Am Montag, 20. April 2015, 15:23:28 schrieb Lentes, Bernd:
> Hi,
> we'd like to create a two-node cluster for our services (web, database,
> virtual machines). We will have two servers and a shared fiberchannel SAN.

> What would you do e.g. with the content of the webpages we offer ? Put them
> on the SAN so we don't need to synchronize them between the two nodes ?

Yes. That seems to be a good idea.

> Also the database and the vm's on the SAN ? Which fs would you recommend
> for the SAN volumes ? OCFS2 ? Can I mount the same volume on each node
> contemporarily ? Or do I have to use the ocfs2 as a resource managed by
> pacemaker, so that the volume is only mounted if it is necessary ?

In your setup I'd avoid concurrent mounts of the columes on both servers. If 
you have concurrent mounts, you will have to use a cluster file system (OCFS2, 
GFS, ...). These file systems provide locking. But if pacemaker takes care, 
that the volumes are only mounted on one machine, you can go with a plain file 
system (ext4, efx).

if you need LVM, you anyway need LVM2 with Distributed Locking (DLM).

Please also consider NFSv4 if your SAN box offers it. NFS has file locking 

Please do not hesitate to mail to me or to the list, if there are any other 

For the databases, you also could consider using a Master/Slave setup. So the 
data replication does happen on application level and no shared filesystems are 
needed. pacemaker handles the state (Master / Slave) of the database 
application. Otherwise the database would need share storage.

Please note that you need fencing in ANY case if you have shared storage.


Mit freundlichen Grüßen,

Michael Schwartzkopff

[*] sys4 AG

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