@olivierlambert You are absolutely right: tags are enough. My fault. We will code some cronjobs that find the current SR, set the right tag and that's it. If the cronjob runs before the CR job is running, we should be fine.
If you will implement the other idea: I guess (as you can specify only one backup target atm) an option to choose: 'store all vdis in target SR' or 'store only vdis from source SR in target SR' would be great, but if less work should be done: just store all vdis in the target SR - no matter where the source vdis are laying around
Anyway: great work! Keep on!