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If you have a look at the following:
It doesn't appear as though HAMMER is designed for desktop systems; it reserves quite a lot of space that it uses for a buffer and you won't get free space back immediately after delete operations - you'll need to wait for the cron jobs to run (that you must set up yourself) before the file system is cleaned up.
It certainly looks like something you would deploy on clustered enterprise hardware but I'm not sure it would replace ZFS on the Mac/FreeBSD desktops any time soon, though I do share your ZFS memory requirements concerns.
The OP wants to use it on a multi-TB fileserver for storing movies and music. Pretty much an ideal use for HAMMER. It's not like you'll be deleting your library all that often.