[ovirt-users] Extending iSCSI storage domain

Hello, I have an oVirt 4.1.1 installion with 2 nodes and an ovirt manager on a serpate machine. I have  multiple storage domain on an external storage, one contains the disk images of VMs, and another is a huge storage domain dedicated to store mediafiles. The mediafile storage domain has only one disk image, attached to a linux vm, no other disk image on this mediafile storage domain. The mediafile storage domain is attached and available to both ovirt nodes. This media storage domain has to be extended. The storage device has the capacity, so it is going to be extended. What should be done on the oVirt side to extend the media storage domain? Sorry for the lame question but the docs and tips from the web are ambiguous for me, some say it cannot be extended, just add a new lun to this storage domain. Does this operation need the full cluster to be put maintenance and stop all vms? Or just the linux vm to that is the disk image is attached to? Thank you for your help! Regards, Peter