That's really cool. There are a bunch of tools that will let you symlink or hard link deduplicate files, but being able to do block-level dedupes simply by leaning on the filesystem is nice.<p>It sometimes feels like games are made to thwart this type of thing. They often use packfiles, basically filesystems within files optimized to look up assets quickly. Also perhaps they allowed optimized data layout from when consoles had slow spinning hard drives. The upshot is that a tiny patch inserting a line of code in a script may offset hundreds of megabytes of other data in the packfiles, causing the block hashes to no longer match up. Do any filesystems model inserts in some way? I'm pretty sure Steam updates can handle situations like that. I frequently see updates which download a tiny amount (kilobytes) but write a huge amount to disk (gigabytes), and I can't think of any other cause. (Assuming developers aren't using hilariously un-compressed assets).