As you scale up your storage, I'd recommend you switch away from RAID-Z to a pool of mirrors (essentially RAID10). It becomes easier to add or upgrade pairs of

As you scale up your storage, I'd recommend you switch away from RAID-Z to a pool of mirrors (essentially RAID10). It becomes easier to add or upgrade pairs of disks with differing capacities (eg, a pair of 1TB, a pair of 2TB...), and in the event of failure you have more than a snowball's chance of being able to rebuild the array before you have another disk go.