When your cluster configuration is complete and you have configure O2CB on both hosts, you can create the actual file system.

To that end, first check your cluster status:

/etc/init.d/o2cb status
	Module "configfs": Loaded
Filesystem "configfs": Mounted
Module "ocfs2_nodemanager": Loaded
Module "ocfs2_dlm": Loaded
Module "ocfs2_dlmfs": Loaded
Filesystem "ocfs2_dlmfs": Mounted
Checking O2CB cluster ocfs2: Online
Heartbeat dead threshold = 31
  Network idle timeout: 30000
  Network keepalive delay: 2000
  Network reconnect delay: 2000
Checking O2CB heartbeat: Not active

Now, use OCFS2's mkfs implementation to create the file system:

mkfs -t ocfs2 -N 2 -L ocfs2_drbd0 /dev/drbd0
	mkfs.ocfs2 1.4.0
Filesystem label=ocfs2_drbd0
Block size=1024 (bits=10)
Cluster size=4096 (bits=12)
Volume size=205586432 (50192 clusters) (200768 blocks)
7 cluster groups (tail covers 4112 clusters, rest cover 7680 clusters)
Journal size=4194304
Initial number of node slots: 2
Creating bitmaps: done
Initializing superblock: done
Writing system files: done
Writing superblock: done
Writing backup superblock: 0 block(s)
Formatting Journals: done
Writing lost+found: done
mkfs.ocfs2 successful

This will create an OCFS2 file system with two node slots on /dev/drbd0, and set the filesystem label to ocfs2_drbd0. You may specify other options on mkfs invocation; please see the mkfs.ocfs2 system manual page for details.

After formatting, opening ocfs2console should display your newly created file system, albeit without a mount point.