Multiple casts of Snow Globe on top of one another stack HP onto the new single globe up until a cap of 1 million HP. This is the entire point of the build, it's meant to hit that cap easily. Start by activating Arcane Tanker then Parasitic Armor for the bonus armor, then start using Snow Globes.

The HP of a single globe can be found by calculating the following:

{Base Health + Armor Multiplier × ([Frost]'s Base Armor × (1 + Base Armor Bonus) + Additional Armor)} × (1 + Ability Strength) + Absorbed Damage

If you add at least one + ability strength Archon Shard onto the frame, that boosts the ability strength to 385% for Tau or 380% for normal Shards. That gives us these two numbers:

{3500 + 5 × (300 × (1 + 1.925) + 6121)} × (1 + 2.8) = 146271.5 HP per cast with normal Shards

or

{3500 + 5 × (300 × (1 + 1.925) + 6185.75)} × (1 + 2.85) = 149442.5 HP per cast with Tau Shards

The additional armor in both expressions is from Parasitic Armor and Arcane Tanker, with Parasitic Armor scaling off of ability strength as well at a 1 to 1 ratio.

Additional Armor = (Shield x Ability Strength) + 1200

Effectively it doesn't matter whether you have Tau shards or not, as long as the globe is at ~145k-150k HP per cast. At this HP it takes 7 casts of 3 to reach the cap of 1 million, not including absorbed damage. The other 3-4 Archon Slots are for maximum energy. With normal Shards your energy max goes to 625 with 4 shards, and with Taus it goes to 650 with only 3 (or 625 with 2 Taus and 1 normal). At 78 energy per cast for both Parasitic Armor and Snow Globe, with 625 or 650 energy you have enough for your 2 and all 7 casts of 3. As long as you start with full energy you can hit 2 then keep hitting 3 until you have a 1 million HP Snow Globe. The only difference between the two is that using Tau Shards saves you a slot for another Archon Shard, but both do the trick. [Energy Siphon] on the aura and Arcane Energize in the other arcane slot are there to help you hit max energy faster. Survivability in the build is lots of armor with a good HP pool from [Umbral Vitality] and of course massive globes.