glabel metadata protection (WAS: ZFS: drive replacement performance)

[Pete French]

> I would say in this case you're *not* giving the entire disk to the 
> pool, you're giving ZFS a geom that's one sector smaller than the disk. 
>   ZFS never sees or can touch the glabel metadata.

Is ZFS happy if the size of it's disc changes underneath it ? I have
expanded a zpool a couple of times simply by changing the size of
the partition and rebooting the machine - it comes up with the new
amount of free space fine. Never tried it the other way though. The
reason I mention it is that someone suggested glabeling a drive in
an existing pool and using replace to swap it over. Which should be good
I guess unless the last sector was in use. ZFS spreads stuff all over the
disc as I unserdtand it though, so that might not be a good assumption,
even on a fairly empty filesystem.

-pete.