One thing you might want to check is if you're setting a limit in the driver for the amount of memory ZFS uses for caching. By default it'll use a LOT of memory

One thing you might want to check is if you're setting a limit in the driver for the amount of memory ZFS uses for caching. By default it'll use a LOT of memory, so I usually just set to a max of 2GB and don't see any issues.