I need to configure 3-node cluster with shared GFS2 filesystem. GFS2 needed as common Documentroot for apache behind the balancer. Can you suggest some guide on how to configure corosync+pacemaker+GFS2 on RHEL/SL 6.1? BTW I don't need DRBD as I have iSCSI as a shared block device.
I haven't seen how 6.1 changes things, I've only done it with 6.0, but this is what worked for me:
At this point you have a cluster. Ensuring the cluster services come on after a reboot is a very good idea at this point.
Now for the GFS side.
When mounting the GFS device, ensure that "netdev" is listed in the options in fstab since GFS can't mount until after the network and cluster is established.
I updated Clusters from Scratch a couple of days ago to reflect the removal of gfs-pcmk. Just ignore the parts about drbd since you have iSCSI.
In particular, you'll want the section starting at: http://www.clusterlabs.org/doc/en-US/Pacemaker/1.1/html/Clusters_from_Scratch/ch08.html which details how to use the 'standard' cman versions of gfs_controld and dlm_control with Pacemaker.
Also keep an eye out for package updates in 6.2, the Pacemaker/CMAN integration gets another boost.