Ok here's what I'd like to do now that I understand it a bit more. Sorry if its a bit long... anyone's help is appreciated. May seem simple but read on.. Desired: Have 2 alternating USB drives for backup targets - one will always be offsite. Create a Full image, once every 2 weeks with Diffs in between. Swap the USB drives out every 2 weeks resulting in 1 Full and 11 Diffs on each USB drive. i.e 2 weeks worth on each. Every 2 weeks I'd like it to start over - not accumuate so not to fill up the drives. This way: - I can go back 2 weeks for recovery - one drive will always have a backup set in case the other dies - or the servers blowup in the middle of backing up to a usb drive. - And keeps insurance happy! sidenote: I don't think going incremental is wise because what if one of them (an incr. file) is bad? Then recovery will fail. Differential takes more space but space is cheap - I think its worth it. And one can use any Diff file with its Full parent. Is this a fair statement? Proposed plan: Any month... Using USB drive 1... Week 1 - Mon is Full backup Week 1 - T, W, Th, F, Sat is Diff. Week 2 - NO new Full. M, T, W, Th, F, Sat is Diff. Using USB drive 2... Week 3 - Mon is Full backup Week 3 - T, W, Th, F, Sat is Diff. Week 4 - NO new Full. M, T, W, Th, F, Sat is Diff. Then back to USB-1 for next month. Fair enuf? So, after the first month, I would have 1 Full backup image for 11 Diffs on each USB drive. Here's what I'm not sure of: 1. In the first month, USB-2 is exchanged for USB-1 on week 3 as normal before the Monday; USB-2 drive is empty so, a new Full image is created on the Monday and new Diffs are created and so on. ok this should work right? 2. What happens at the start of the 2nd month when USB-1 is put back? Can the scheduling handle the fact that for instance, USB-1 has been "away" for 2 weeks? Will it be "remembered"? Will Acronis be confused or continue (as desired) and overwrite the Full backup with a new one and Diff overwrite the diffs etc? Again, I don't want Acronis to create new image files and fill up the drive Lastly.... sorry to be long winded... but I don't want to try this if it won't work.. no time! - If for instance, USB-2 was forgotten about and USB-1 were left connected for the entire month or more; I need to be sure that the Full image will overwrite itself every 2 weeks and same for the Diffs every week - so the drive doesn't fill up. i.e. it won't be disaterous if the drive swap is forgotten. Hope this is not too complicated... If the acculated space from the Diffs proves to be too big, I can probably reduce it to every second day for Diffs. The main thing is to have 2 drives in the plan with one always offsite. Thanks for you patience and assistance.