With Tape backups one would follow a schedule of frequent interim backups with long term backups interspersed. The interim tapes would be re-used later.
I suppose that with an external hard drive the goal is have a nearly real time (external) backup of whatever is on the source drive. In that case, I would expect to keep the one backup of each source until that source expires, at which time the backup would be frozen indefinitely. If there is enough extra space on the backup medium, it might be used to backup another volume.
Actually, I use USB thumbdrives or network resources for synchronization, which I consider to be between two or more computers. External drives are not always the most convenient medium for that purpose. Cloud drives are convenient but not secure port to port, regardless of whether one can trust the provider no to lose or share anything with advertizers, crooks or governments. The difference between the last two is sometimes difficult to detect.
However, if crippled software has created multiple backups of the same volume, using up the entire terrabyte of space backing up one 300 Gig hard drive, I want to recover the wasted space.
I believe that interim backups and multiple undesired backups need to be deletable.
Perhaps Western Digital wants to sell more hard drives by making them work like write-once CD’s. They should sell them in 10-packs.
