NFS / Network Filesystem Stall
NFS stalls freeze training when the storage server becomes unresponsive.
NFS stalls freeze training when the storage server becomes unresponsive.
What this failure is
NFS / Network Filesystem Stall is a Infrastructure failure seen during ML training runs. NFS stalls freeze training when the storage server becomes unresponsive. Common tags: Nfs, Network, Storage, Stall.
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Why it happens (the mechanism)
NFS server overloaded with training writes. Network congestion between compute and storage nodes. NFS namespace conflict from concurrent writers. NFS server crash or restart. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- Checkpoint operations hang indefinitely
- File reads and writes timeout
- Training appears frozen but process is alive
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| File operations hang at NFS mount points | NFS server overloaded with training writes |
| ls /mnt/checkpoints hangs indefinitely | Network congestion between compute and storage nodes |
| kernel: NFS: server not responding, still trying | NFS namespace conflict from concurrent writers |
| Training stalls at checkpoint save or log write | NFS server crash or restart |
Which systems are affected
- Training with NFS-mounted checkpoint directories
- NFS-mounted home directories for code
- Multi-node all writing to same NFS target
How to confirm this is the problem
Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: File operations hang at NFS mount points
- ✓Verified signal present: ls /mnt/checkpoints hangs indefinitely
- ✓Verified signal present: kernel: NFS: server not responding, still trying
- ✓Verified signal present: Training stalls at checkpoint save or log write
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Root cause
- NFS server overloaded with training writes
- Network congestion between compute and storage nodes
- NFS namespace conflict from concurrent writers
- NFS server crash or restart
The fix and how to prevent it
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