ZFS pool restructuring and emergency repair

[Quartz]

> I hate to jump in and be "that guy" but, seriously, if you are using
> this for something crucial, are you really going to risk it all with "an
> old 500GB"? Drives aren't so expensive that you can't afford to buy a
> spare match to keep on the side until such a day occurs.

That's a fair point, but the question here is "catastrophic emergency" 
that takes out all of your spares and you have to limp by on something 
you found under the couch for a day or two until you can get new drives 
in. You can imagine whatever contrived situation is most likely in your 
case.

My main concern is that ZFS is just kinda inflexible about some things, 
(especially disk/pool configurations) and that has the potential to 
cause real problems in some situations. I've seen a lot of things happen 
against the odds through the years, so I like to plan ahead as much as 
possible and try to figure out what my options are for mitigating those 
risks. Part of that means periodically asking around to see what's 
changed that I might have missed.