Comment by mustache_kimono

> As far as I understand, ZFS doesn't work at all with disks of differing sizes (in the same array).

This might be misleading, however, it may only be my understanding of word "array".

You can use 2x10TB mirrors as vdev0, and 6x12TB in RAIDZ2 as vdev1 in the same pool/array. You can also stack as many unevenly sized disks as you want in a pool. The actual problem is when you want a different drive topology within a pool or vdev, or you want to mismatch, say, 3 oddly sized drives to create some synthetic redundancy level (2x4TB and 1x8TB to achieve two copies on two disks) like btrfs does/tries to do.