(25-09-2016, 12:55 PM)vain Wrote: I used to do what most people do: Attach a USB drive or boot up my NAS, and then backup data using rsync. The thing is, how do you know that the files you're backing up are actually intact? How do you verify that you're not creating the 8th backup in a row of a file that has been corrupt for two weeks? Backups are worthless if you should have restored a file from the old backup instead of creating a new corrupt backup.

You're touching one big concern.
It's the same concern people have when sending data over anything.
That's the reason we have checksums that come with big ISO files.

(25-09-2016, 12:55 PM)vain Wrote: The third issue is: How can you efficiently verify that your backups aren't corrupt?

(25-09-2016, 12:55 PM)vain Wrote: https://github.com/ambv/bitrot
It's basically "sha1sum on steroids". It makes it easy to scan large data sets, compute checksums, and verify them later. There are other tools like it. Maybe for your use case, sha1sum actually is good enough.

Yep, I've tried it, it's pretty nice.
I like the idea of keeping track of changes in bulk.
I'm not sure it's the best way but it's a good approach.

(25-09-2016, 12:55 PM)vain Wrote: Even today, USB sticks fail very often. Still, nobody really cared ...

If you don't plug a USB stick for a while the data on it fades away.
Every technology is a time bomb.

Probably incremental backups with diffs can solve this.
Maybe by showing the diffs, like rsync with the verbose option.