[derefr]

I don't need backups of my (S3) backup, because it's more likely my personal backup process has a flaw such that it will backfire and destroy my data, than that it will one day save it from the inadequacy of Dynamo's ~RAID17.

Consider: each time you introduce a new device that has local, physical access to the place your data lives, that's one more thing that could Halt and Catch Fire at just the wrong time, or be replaced with a USB Killer or a DMA cryptolocker device by social engineering. If it involves data center operators you don't know, that's more people you have to trust not to break whatever they touch or have been paid off to steal your corporate secrets. Etc.

Sure, the probabilities are small—but so is the probability of the great data fortresses crumbling to ash and you being the Last Best Hope for your data. Hypothetical ameliorations of sub-lightning-strike probabilities often have failure modes more likely than their use.

[jacquesm]

In that case I hope you have your S3 under a different account than your main stuff. There are more reasons why stuff goes missing than just hardware failure.

Note that a backup need not make things worse, but should only make things better.

[icebraining]

Consider: each time you introduce a new device that has local, physical access to the place your data lives

Right. So don't do that. Put it somewhere else, and configure the original device to push to it rather than give the new device access to the original. You can use a service that implements the S3 API, then you don't even need to install new stuff on the original, just configure an extra endpoint. Also, encrypt before pushing (that counts for S3 too).