I just found a weird things on they ToS [1] ... 8. Our service may automatically delete a piece of data you upload or give someone else access to where it determines that that data is an exact duplicate of original data already on our service. In that case, you will access that original data. Duplicate check, I get that. But, how do they do it? They say the files are encrypted on the browser, so if I upload file X an…
Maybe they use block deduplication on the storage arrays? Particularly looking at the "our service may automatically delete a piece of data you upload". In other words, you already uploaded it encrypted and they're just serving out the de-duplicated bits.
Encrypted data is indistinguishable from random data, so it is incompressible. The chances of finding anything significant to deduplicate are so low that it's not worth trying.