Sun の中の人のコメント

[zfs-discuss] Re: Shrinking a zpool?
http://mail.opensolaris.org/pipermail/zfs-discuss/2006-April/002064.html
A similar feature exists on VxVM to re-layout storage. It has a lot
of value in certain circumstances mostly revolving around migrating
from one storage solution to another.

However, that feature didn't arrive until years after the initial
product rollout. I think that having a stable product is more
important in the short term than having a product with every feature.

Once ZFS has been out (and on the system disk!) a year, the feature
should be in the product.