In that case, I did not just describe tarsnap, or at least - did not intend to.
bup _is_ designed for backup rather than random access. But it is easy enough to make those backups look like read-only file systems (bup includes an FTP server, HTTP server and FUSE module that expose a backup set through the respective protocol or as a filesystem).
But since bup builds on git, and a bup backup set is actually a git repository, you get all the git related stuff for free - e.g. bup supports cryptographic signatures in the repository by way of git's signing support -- although, for now, the "bup" command does not implement them (so, if you want to sign or verify the signature, you'll have to use git on the repository rather than bup)
Bup's deduplication is comparable to rsync's (and it reuses rsync's main tool for that). If you change a byte in the middle of a 100MB file, you'll likely need to transfer ~16k to or from backup (compared to the other version of the same file). That's also true if a byte was inserted in the middle of the file. And if you backup 100 copies of a 100MB file, was just a few bytes changed in each file compared to each other file - you'll need less than 150MB of space/storage, rather than the 10GB or so without deduplication.
bup _is_ designed for backup rather than random access. But it is easy enough to make those backups look like read-only file systems (bup includes an FTP server, HTTP server and FUSE module that expose a backup set through the respective protocol or as a filesystem).
But since bup builds on git, and a bup backup set is actually a git repository, you get all the git related stuff for free - e.g. bup supports cryptographic signatures in the repository by way of git's signing support -- although, for now, the "bup" command does not implement them (so, if you want to sign or verify the signature, you'll have to use git on the repository rather than bup)
Bup's deduplication is comparable to rsync's (and it reuses rsync's main tool for that). If you change a byte in the middle of a 100MB file, you'll likely need to transfer ~16k to or from backup (compared to the other version of the same file). That's also true if a byte was inserted in the middle of the file. And if you backup 100 copies of a 100MB file, was just a few bytes changed in each file compared to each other file - you'll need less than 150MB of space/storage, rather than the 10GB or so without deduplication.