Only if your provider is doing it in the ridiculous and naive manner suggested in the post.

Oh of course, but I can see it being used fairly widely since it does have (esp on larger networks) the obvious advantage of being able to save a LOT on hardware if a lot of stored data is duplicates.

I don't think a lot of backup providers do this but file-mesh services and file sharing services surely do.

My point is specifically that many of them are doing so in this ridiculous way. You can try for yourself: upload a bunch of pirated mp3s and see if the transfer is suspiciously fast.

But saying that other companies are doing things wrong, doesn't mean you have to throw the baby out with the bathwater - you can still do de-duping, you just won't do it in a way that exposes vulnerabilities/etc.

The article makes it sound like it cannot be done.

To my knowledge, it cannot be done in a way that addresses the privacy concern: that a court could require the storage operators to answer such questions about their customers as described in the article.

If there's a way around that, I am your eager student.

By the way, some people have suggested using reference counts as a solution. You then know, for example two or more users share duplicate data, but not which two users. My feeling is that, at some time, you did know which users those were (when the counts were incremented.) I like to stay within the realm of "we are not capable of knowing" instead of simply, "as it happens, we don't know anymore."

As long as they have the files in plaintext, I prefer the 'ridiculous' method for the speed benefits. If you upload data unencrypted and expect perfect privacy on it you're fooling yourself.

SpiderOak encrypts your files before upload, and they don't have the keys. ( https://spideroak.com/whyspideroak )

Thats why at the end of the post they say that even if they decided to deduplicate in the future, they would have no way of retroactively doing it.

Yes, SpiderOak does, but I'm talking about the ones being complained about.