ZFS内存占用大的原因是带内去重吧……

BTRFS这边说

Inband / synchronous / inline deduplication is deduplication done in the write path, so it happens as data is written to the filesystem. This typically requires large amounts of RAM to store the lookup table of known block hashes. Patches are currently being worked on and have been in development since at least 2014. See the User notes on dedupe page for more details.

实际上也是我用BTRFS的时候并没有感觉有多吃内存,果然是因为没有带内去重吧……