[stewartbutler]

You can build it, but it is limited to the smallest device in the vdev, so the array will appear to only have three devices of 64m available. Though you can replace all smaller disks and grow it.

[Annatar]

That is not how RAIDZ works. Because every write is a dynamic width stripe, the capacity is an aggregate minus parity, not linear.

The smallest device capacity applies to RAID1+0, which is mirroring, but it does not apply to RAIDZ.