When a filesystem is protected against concurrent mounting, and a second mount attempt is made you will see this error:
# lsfs -q /mountpoint
Name Nodename Mount Pt VFS Size Options Auto Accounting
/dev/fslv34 -- /mountpoint jfs2 4194304 rw no no
(lv size: 4194304, fs size: 4194304, block size: 4096, sparse files: yes, inline log: no, inline log size: 0, EAformat: v1, Quota: no, DMAPI: no, VIX: yes, EFS: no, ISNAPSHOT: no, MAXEXT: 0, MountGuard: yes)
# mount /mountpoint
mount: /dev/fslv34 on /mountpoint:
Cannot mount guarded filesystem.
The filesystem is potentially mounted on another node
After a system crash the filesystem may still have mount flags enabled and refuse to be mounted. In this case the guard state can be temporarily overridden by the “noguard” option to the mount command:
# mount -o noguard /mountpoint
mount: /dev/fslv34 on /mountpoint:
Mount guard override for filesystem.
The filesystem is potentially mounted on another node.
