72-GPU Blackwell Ultra MRC Rack — Arista 7060XE7 + Nvidia HGX B300 9 × HGX B300 (72 B300 GPUs) · 8× CX-8 SuperNIC per node @ 800G · 8 MRC planes · 16× 7060XE7 · 57.6 Tbps aggregate Server Rack 9× HGX B300 · 72 Blackwell Ultra GPUs MRC Fabric — 8 independent planes Arista 7060XE7 · 800G per uplink · no cross-plane links P1 P2 P3 P4 P5 P6 P7 P8 Spine P1 Spine P2 Spine P3 Spine P4 Spine P5 Spine P6 Spine P7 Spine P8 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 ← fully independent planes — no cross-plane links → Leaf P1 Leaf P2 Leaf P3 Leaf P4 Leaf P5 Leaf P6 Leaf P7 Leaf P8 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 7060XE7 HGX B300 #9 — GPU 65–72 8× B300 · NVSwitch5 1.8TB/s · 8× CX-8 SuperNIC @ 800G 800G×8 HGX B300 #1 — GPU 1–8 8× B300 · NVSwitch5 1.8TB/s · 8× CX-8 SuperNIC @ 800G 800G×8 Upgrade: CX-7 400G → CX-8 800G · same MRC discipline · 2× fabric BW 72 B300 GPUs 9× HGX B300 72 CX-8 SuperNICs 800G each · 1:1 GPU:NIC 16 7060XE7 switches 8 leaf + 8 spine 57.6 Tbps total fabric 9 nodes × 6.4 Tbps (8×800G) 2 hops any-to-any leaf → spine → leaf 2× fabric vs H100 rack 28.8 → 57.6 Tbps Cable = plane: P1 P2 P3 P4 P5 P6 P7 P8 · CX-8 NIC n → leaf of plane n · 32-bit EV in SRv6 uN SID · 128–256 EVs/QP · no ECMP · no dynamic routing · liquid cooling req · 1,400W TDP