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llama.cpp · homogeneous 2–4 GPUs · not a PC builder

Can this model run across multiple GPUs?

Phase 8 answers memory feasibility for identical cards under llama.cpp. Default split is layer (pipeline parallel: each GPU owns a slice of layers; KV stays with those layers). This is not 2 × VRAM = pool, and it is not a complete PC build.

2× AMD Radeon RX 5500 XT 8 GB

Does not fit on this configuration

Model
GPT-OSS 20B · Q4 · 8K
Runtime / split
llama.cpp · layer · calculator 1.0.0
Single-GPU status
CPU_RAM_OFFLOAD_REQUIRED · required 14.7 GB vs usable 7.2 GB
Per card advertised / usable
8 GB / 7.2 GB
Aggregate advertised
16.0 GB — capacity, not effective model capacity
Nominal aggregate usable
14.4 GB (N × advertised × 0.90)
Effective per-GPU peak
7.7 GB vs usable 7.2 GB
Per-GPU split (approx.)
weights 6.3 GB · KV 0.2 GB · runtime 0.8 GB · safety 0.4 GB
Why
Even a 2K context exceeds per-GPU usable VRAM after partition and per-device reserves.
Topology
Requires space for 2 discrete GPUs. Exact cooler slot width is not in the RigForAI graph. layer split is pipeline parallel and can run over PCIe. KV stays with the layers on each GPU. NVLink is not treated as a 1× aggregate VRAM pool.
Performance
Phase 5 predictions are single-GPU. Multi-GPU tok/s is not published.
GPU-only current cost
$499.98 = 2 × $249.99 at the current per-card matched price. This does not mean 2 units are in stock, and it is not a complete build cost.
MSI GAMING RX 5500 XT X 8G AMD Radeon RX 5500 XT 8 GB GDDR6 · ASIN B082G34GSL
Amazon
Formula
per_gpu_peak = ceil(weight_bytes/N) + ceil(kv_bytes/N) + runtime_base + safety_base + weight_fractions×ceil(weight_bytes/N). Compare to usable = advertised×0.90. Not (single_gpu_required × N) and not advertised_vram × N as effective capacity.

AMD Radeon RX 5500 XT 8 GB · Single-GPU can-run · Find a single GPU · Build a machine for this GPU setup

Query combinations are not indexed. Source: llama.cpp multi-GPU documentation.