3 disk RAID1?

[Mark Knecht <markknecht@gmail.com>]

Hi all,
   I'm still very much on a steep learning curve about what I can do
with Linux software RAID. In another thread this weekend a couple of
responders discussed among themselves 3-disk RAID1 solutions that can
survive if 2 disks die. I don't understand what that means. Can
someone point me at a quick explanation? Is that really possible?

   In general I'm using a few Wikipedia pages and gravitate toward the
diagrams as much as anything.

http://en.wikipedia.org/wiki/RAID
http://en.wikipedia.org/wiki/RAID1#RAID_1

RAID0 - striping, speed not reliability (2 disk minimum)
RAID1 - duplicate data, no other protection (2 disk minimum)

   How do I build RAID1 using three drives? Just duplicate the data 3
times? If drives start going bad how do I determine which one or two
are failing? (fsck? SMART?) With 3 drives 1 fail seems relatively
straightforward to figure out, but 2?

Thanks,
Mark