[Fedora-xen] Raid-1 over iscsi vs DRBD?

[Chris Hirsch]

Hey all...I'm looking to set up a high availably xen "cluster" so that
if my iSCSI storage goes down, my domU's will remain up. I've been
looking around on the net and it appears this is a pretty common thing
to do but I have one question that I haven't seen an answer to.

It looks like I can accomplish the high availably in one of two ways. I
can use DRBD on my two boxes as shown here
http://www.gridvm.org/drbd-lvm-gnbd-and-xen-for-free-and-reliable-san.html
and I should be able to take down a storage box and my iSCSI domU's will
never know any difference.

An alternate approach (as I see it) is that instead of DRBD  I should be
able to carve out two iSCSI targets (one on each storage machine) and
then in my domU make those two targets (say sda1 and sdb1) a raid-1 and
accomplish the same thing as DRBD but use the Linux md stuff instead? Is
there a reason that this isn't done? From my lack of findings I'd say
yes but  I haven't actually tried this in a real setting yet. I was just
hoping somebody could steer me in the right direction (and away from
this approach if it's just silly). My *guess* is that DRBD was written
to do a network raid-1 and thus has optimizations to do just that vs a
Linux "disk" raid-1 using md.

Thanks for any pointers or insights to this. I'd really appreciate any
websites or writeups that would compare the two or just some cook book
examples.

Thanks,
Chris