ZFS - whole disk or partition or BSD slice?

[Warren Block]

On Mon, 28 Jan 2013, Steve O'Hara-Smith wrote:

> 	There's one other good reason to use partitions when mirroring.
> When the time comes to replace a drive in a mirror it is necessary that the
> new drive be the same size (or larger) than the one it replaces. Given that
> drives of nominally the same capacity (and even of the same type and brand
> bought at different times) tend not to be exactly the same size using a
> partition a little smaller than the whole drive makes it certain that a
> replacement drive will be big enough to use in the mirror when it arrives.

The claim is that newer versions of ZFS leave some unused space at the 
end of the drive to allow for slightly different nominal sizes.  I have 
not yet found any references to what versions or how much space.