Fine-Tuning an LLM on H100 GPUs for Under £100: What You Need to Know
Large language model fine-tuning has a reputation for being expensive. But with the right approach — LoRA adapters, a single 8× H100 cluster run, and £GBP-billed pay-as-you-go compute — you can fine-tune a 7B parameter model for under £100 total. Here’s exactly how.
Why LoRA Changes the Economics
Full fine-tuning updates every parameter in the model — expensive and memory-hungry. LoRA (Low-Rank Adaptation) instead trains a tiny set of adapter weights alongside the frozen base model. For a 7B model, LoRA reduces trainable parameters by over 99%, cutting GPU memory usage from ~140 GB to under 40 GB — making it possible on a single A100 80GB.
The Real Cost Breakdown
Quick-Start Commands
# Install dependencies
pip install transformers peft datasets mlflow
# Launch LoRA fine-tune on HuggingFace model
python train.py --model_name mistralai/Mistral-7B-v0.1 --lora_r 16 --lora_alpha 32 --num_train_epochs 3 --per_device_train_batch_size 4💷 Cost tip: Use the 8× H100 SXM cluster at £14.99/hr only for the training run itself. Switch to a T4 at £0.28/hr for evaluation and notebook experimentation — that alone saves ~£40 on a typical fine-tuning project.
Key Takeaways
- LoRA + HuggingFace PEFT is the fastest path to affordable fine-tuning
- MLflow tracks every experiment automatically on Rooting Clouds with zero setup
- Pay-as-you-go means your total cost is your actual training hours — not a monthly reserved instance
- UK data residency keeps sensitive training data on British soil by default