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Downloading Files

You can download files from external sources using the download_file function. This function handles downloading files from URLs with built-in caching and error handling. This is particularly useful for downloading datasets, configuration files, or any external resources your application needs. 
from fal.toolkit import download_file, FAL_PERSISTENT_DIR


class MyApp(fal.App):
    def setup(self):
        path = download_file(
            "https://example.com/myfile.txt",
            FAL_PERSISTENT_DIR / "mydir",
        )
        ...

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Downloading Model Weights

You can download model weights from external sources using the download_model_weights function. This function is specifically designed for downloading model weights and provides several useful features:
  • Predefined storage location: Automatically stores weights in an optimized directory structure
  • Smart caching: Avoids re-downloading weights that are already present unless forced
  • Authentication support: Supports custom request headers for private repositories
This function is particularly useful for downloading pre-trained model weights from Hugging Face, custom model repositories, or private storage locations. 
from fal.toolkit import download_model_weights


class MyApp(fal.App):
    def setup(self):
        path = download_model_weights(
            "https://example.com/myfile.txt",
            # Optional: force download even if the weights are already present
            force=False,
            # Optional: specify request headers
            request_headers={
                "Authorization": "Bearer <token>",
            },
        )
        ...

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Improving Hugging Face download speeds

The Hugging Face library caches files locally to prevent duplicate downloads. Within Fal, this cache is automatically placed on the /data persistent volume via the HF_HOME environment variable that is set to /data/.cache/huggingface. The steps below offer additional speedups.

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Set Hugging Face token

Ensure you have your Hugging Face token set to be used by Fal runs. Authenticated downloads seem to be faster than anonymous ones: fal secret set HF_TOKEN=xxx

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Save weights to the /data volume

Hugging Face weights need to be stored within the /data volume. This:
  • Speeds up runner starts by removing the need for files to be reconstructed from the cache (which is already on /data)
  • Ensures enough disk space is available
snapshot_download(
    repo_id=model_id,
    local_dir="/data/models/deepseek-ai",
    ...
)

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Speed up initial weights downloading

Depending on the size of the weights, the initial call to snapshot_download can take a while. Hugging Face seems to reduce download speeds for large models after some time. While individual transfer thread often start at 50+ MB/s, after a while the speed drops to 5-6 MB/s. There are 3 ways to speed up downloads:
  • Increase concurrency, max_workers and cache size: 
    os.environ["HF_XET_HIGH_PERFORMANCE"] = "1"
os.environ["HF_XET_CHUNK_CACHE_SIZE_BYTES"] = "1000000000000"
os.environ["HF_XET_NUM_CONCURRENT_RANGE_GETS"] = "32"

snapshot_download(
    repo_id=model_id,
    local_dir=model_dir,
    max_workers=32
)
  • Download many models in parallel: when downloading multiple models, it helps to start a separate Fal run for each one. The different source IP address reduces the risk of rate limiting.
  • Restart slow downloads: restart the run after e.g. 10 minutes, which will likely cause it to go to a different physical server, and the download will resume at higher speeds.

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Speed up model files check

Even after fully caching weights, calling snapshot_download with a large model can sometimes take 45+ seconds. The Hugging Face library takes this time to do API calls and metadata checks. You can use local_files_only=True to skip this step, which typically makes the call return in less than 1 second. Using local_files_only=True will throw an error if the files are not completely cached. To prevent that, it is a good idea to wrap the call in a try/catch block and retry it without local_files_only: 
from huggingface_hub.errors import LocalEntryNotFoundError

try:
    snapshot_download(
        ...
        local_files_only=True,
    )
except LocalEntryNotFoundError:
    snapshot_download(
        ...
    )

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Speed up model loads

Hugging face models are typically split into multiple files, and loading them happens serially. This is sub-optimal if the files are not cached locally as they will be fetched one by one. It is advisable to pre-read all the files in parallel which will create missing caches concurrently, at much higher speeds. Please refer to Sequential vs parallel reading.
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