[Users] iSCSI and snapshots

Hi, I'm trying to understand how ovirt manages snapshots to start using them for vm backups. I have my vms to use a iscsi LUN for the system (each has its own) and I have no extra space to create an LVM snapshot in the VM disk. When I hit "create" in the vm snapshot tab, it creates the snapshot and reports ok, but I see no info in the right pannel (disk, ram,etc) and nothing is created in the data storage of the DC, so I don't get where is ovirt storing the snapshot data. Do I have to create an export storage domain?. Regards, Juan Pablo