Backup utility for NAS units

Hi There, I've been looking around for a program to backup all the data on my 4 NAS units (Each at 5TBs). Unfortunately I can't find a program that does everything I need so I'm looking at a custom program. I have the following goals: 1. Backup all data on all 4 NAS units over the network (by connecting to mapped drive) 2. All data is to be backed up to 7 (or more) 3TB USB disks so the program will need to be able to recognise when a disk is full and it needs a new disk inserting 3. The program has to record (access DB fine) which data is backed up to which USB disk 4. Occassionally I will replace/ammend data on the NAS units so when backing up to USB disk the program has to remove the old data and replace it with the new 5. If Either a NAS unit or a USB disk fails the program should be able to recreate either from the data on the NAS or the USB disk 6. Deletions from the NAS units should be replicated on the USB disks Please contact me for more information if required. Regards rob