We use 2 Disc Priests, 2 Holy Pallies, 2 Resto Druids and a Resto Shaman to heal Anub.
We have two warrior tanks tanking two Burrowers each, and a Feral Druid tanking Anub.
One pally goes on each warrior with Beacon on the MT Druid and the Shaman spends the whole fight healing the druid.
For P1 the Disc Priests just DPS as there is such minimal damage, when the first set of Burrowers spawn and get moved next to Anub we PI our mages/spriests andcontinue using it on CD when the adds spawn again.
P2 is done pretty much different with each guild and as priests we dont do anything interesting this phase. Gogo hand of protection.
P3 is the first fight where stacking disc is beneficial. P3 is all about controlled healing, so thats why we can get away with stacking. Our RL using an addon that marks the 5 penetrating colds.
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http://img27.imageshack.us/img27/72/...0409195321.jpg)
The other priest and i get two marks assigned to us and our shadow priest shields the other mark to be safe. The druids roll hots on each mark and the Disc Priests flash heal/penance if neccessary their marks. The spriest helps out basically as insurance if people get overlapping Colds or if the targets Frost Pot or Healthstone is on CD.
Basically, with FRR Aura up Cold will tick for 4-5k. Penentrating Cold takes 3 seconds after application to do damage, because your raid will be kept at 1kish they'll die if they dot get a PWS or use a Frost Pot/ Healthstone. For that reason we are pretty much the difference between killing the boss and wiping.