[ClusterLabs] principal questions to a two-node cluster

Andrei Borzenkov arvidjaar at gmail.com
Mon Apr 20 23:48:04 EDT 2015

В Mon, 20 Apr 2015 15:36:49 +0200
Michael Schwartzkopff <ms at sys4.de> пишет:

> 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).

Only if you want LVM groups to be active concurrently on both nodes. For
active/passive setup where resources are ever active on one node only
normal LVM is should be fine.

> Please also consider NFSv4 if your SAN box offers it. NFS has file locking 
> included.
> Please do not hesitate to mail to me or to the list, if there are any other 
> problems. 
> 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.

You always need fencing. Shared storage or no shared storage.
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