> Are you using rsync.net's "hidden" attic/borg option? This makes the price very attractive.

I am, yes, and it is quite attractive.

> You mention using "attic check" to guard against bitrot on the provider's storage. How is this in terms of bandwidth used? Does it have to transfer every byte or does it compute a checksum on the encrypted data (since rsync.net doesn't have the raw data) and just send that?

It's very bandwidth-efficient, but I have stopped doing that every day, as rsync.net told me they use ZFS and scrub their arrays regularly, so they would discover bit rot early. I only run the check once a month now.

(attic) borg check --repository-only does not transfer any data except informational logs. This is CRC32 only [1]. Borg 1.1 beta has borg check --verify-data, which does full decryption & full MAC + ID checks -- by downloading all data.

Generally speaking, attic has at least one data corruption bug fixed in Borg that make it unsafe to use with remote repositories unless the SSH connection is 100% stable. Attic also has another similar bug that corrupts the created archive when it encounters an I/O error in the repository.

There is a "Migrating from Attic" "sales pitch" (if you like) in the beta docs (-- switch versions in the lower left corner for stable docs): http://borgbackup.readthedocs.io/en/latest/faq.html#migratin...

[1] and of course checksumming and error correction of the file system, if any. Since rsync.net is ZFS the --repository-only check is a stronger than on a plain old file system with no checksums.