@jstatepost Because you're not booting from this disk, you won't need a EFI partition at the beginning. As far as format - I'd say that depends on what you need it to do. I personally feel ZFS w/o at least setting up a mirror doesn't make much sense. EXT4 would probably work fine.
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@techaddressed @jstatepost Same setup here, just ext4 (+ encryption because it's quite ) portable.
Works fine since years.
