With even distribution you should be fine on the shields. On our kill last night (25 man) we put range in the furthest, heals and the extra ranged in the mid ranged, and melee and offtank in the melee shield, and I (prot pal) stood out for the whole thing since its physical dmg and good SoTR uptime i took basically no dmg from it and whatever aoe heals caught me was plenty, freeing up another spot in a shield in case it was needed.
the shield does not make you immune from his damage. It reduces damage taken. Your raid still need to setup AoE heal CD for each. There are 3 shields, you need to assign 3 on each, with the tank/offtank staying out depending on who the current tank is.
The unmitigated damage is ~120k on me(Hunter with Iron Hawk talent), -40% from that and you get about 70k damage per second, it is still very high, and you cannot outheal it completely and will most likely end up with players having under 20% life after it ends.
It is pretty insane until you sort out the raid CDs.
Make sure your healers have a rotation of CDs figured out before going into the phase. Or at least make sure they can communicate and figure things out on the fly. Once we got it in peoples' heads that they needed to use personal defense cooldowns, it was a lot easier to survive. I think just about every class should have something to make it much easier on the healers. I know, as the tank, I can survive just by using a cooldown without receiving any outside heals. I believe our mage has iceblocked through one. Our rogue uses feint, which is quite effective. This phase shouldn't just be up to the healers to get through.
Yup, yup. We know that it doesn't mitigate all of it, but it actually didn't mitigate anything, when we disbanded the raid and did some group jumping around we tried it again and it worked as intended and he went down.