[datastack]

I agree it seems more common. However back-up time and data movement should be equivalent if you follow the algo steps.

According to chat GPT the forward delta approach is common because it can be implemented purely append only, whereas reverse deltas require the last snapshot to be mutable. This doesn't work well for backup tapes.

Do you also think that the forward delta approach is a mere historical artifact?

Although perhaps backup tapes are still widely used, I have no idea, I am not in this field. If so the reverse delta approach would not work in industrial settings.

[jiggawatts]

Nobody[1] backs up directly to tape any more. It’s typically SSD to cheap disk with a copy to tape hours later.

This is more-or-less how most cloud backups work. You copy your “premium” SSD to something like a shingled spinning rust (SMR) that behaves almost like tape for writes but like a disk for reads. Then monthly this is compacted and/or archived to tape.

[1] For some values of nobody.