dbrady wrote:… It's recommended that in most cases you should not share a disk with ZFS and another file system -- particularly with HFS+. Since HFS+ has a single global lock for all metadata updates (held across the I/O) it is highly sensitive to disk latencies. So for a typical HDD you won't want to share a disk. In the case of your Air with an SSD, you could share with less performance impact than an HDD. If file system performance is less of an issue for you, the ''zpool create'' command will let you use a partition (e.g. /dev/disk2s3) even tough we recommend passing a whole disk slice (e.g. /dev/disk2).
One phrase caught my eye:
Since HFS+ has a single global lock for all metadata updates (held across the I/O) it is highly sensitive to disk latencies
For further information I was referred to What's wrong with HFS+ on page twelve of nineteen of Mac OS X 10.7 Lion: the Ars Technica review | Ars Technica (2011-07-20).