On ZFS you can have multiple vdevs of different sizes in the same pool, and you can also set copies=N to have multiple copies of the data available for extra re

On ZFS you can have multiple vdevs of different sizes in the same pool, and you can also set copies=N to have multiple copies of the data available for extra redundancy. You can't unfortunately tell it that different disks have different speeds. It also works just fine w/ a small (1GB or so) ARC if you want, just at an obvious performance penalty compared to having a larger cache.