For online deduplication you are correct, but there is not much need for online deduplication on a mostly read-only system. BTRFS currently only supports offli

For online deduplication you are correct, but there is not much need for online deduplication on a mostly read-only system. BTRFS currently only supports offline, and I believe the current state of ZFS is only online. A curious situation, but I imagine ZFS will eventually support offline dedupe and with that, the memory requirements will fall in terms of what needs to be cached. And memory usage would decrease, because offline dedupe on read-only files reduces duplication in cache. Even memory-only deduplication would be sufficient. I'm not sure if zswap/zram/zcache support it, but it seems like a worthwhile feature.