As quesera noted below, on a not-so-big modern disk with 500,000 files, the metadata can easily be in the 50-100MB range, which adds up to >1GB for metadata (even when nothing has changed) if you back up every hour.<p>You should, however, consider bup (<a href="https://github.com/bup/bup" rel="nofollow">https://github.com/bup/bup</a>) - it takes less than a minute to figure out nothing is done, it deduplicates <i>parts</i> of files, (that is, if you have a 20GB virtual machine image, and you've changed one byte in the middle of it, then the next snapshot is going to take ~10KB, not 20GB). The older release don't keep ownership/modification time, but there's a new version pending release soon that does.<p>It also works well remotely (through ssh), can do an integrity check (bup fsck), redundancy (using par2; important after deduplication). And it has a fuse frontend that makes it all accessible as a file system, as well as an ftp frontend.<p>bup is teh awesome.