PyTorch Save Failed / Write Error
Checkpoint save fails when disk writes are interrupted.
Checkpoint save fails when disk writes are interrupted.
What this failure is
PyTorch Save Failed / Write Error is a Data Integrity failure seen during ML training runs. Checkpoint save fails when disk writes are interrupted. Common tags: Checkpoint, Save, Storage, Io.
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Why it happens (the mechanism)
Disk full on checkpoint directory. NFS timeout interrupts the write. Filesystem becomes read-only. Checkpoint killed by SIGTERM before write completes. 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
- torch.save() raises OSError during checkpoint write
- Save succeeds but resume fails
- Training crashes losing checkpoint progress
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| OSError: [Errno 28] No space left on device | Disk full on checkpoint directory |
| RuntimeError: Unable to open file for writing | NFS timeout interrupts the write |
| IOError: Read-only file system during checkpoint save | Filesystem becomes read-only |
| Checkpoint file is 0 bytes after save completes | Checkpoint killed by SIGTERM before write completes |
Which systems are affected
- Training with frequent checkpointing
- NFS-mounted checkpoint directories
- Preemptible instances with ephemeral storage
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: OSError: [Errno 28] No space left on device
- ✓Verified signal present: RuntimeError: Unable to open file for writing
- ✓Verified signal present: IOError: Read-only file system during checkpoint save
- ✓Verified signal present: Checkpoint file is 0 bytes after save completes
- ✓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
- Disk full on checkpoint directory
- NFS timeout interrupts the write
- Filesystem becomes read-only
- Checkpoint killed by SIGTERM before write completes
The fix and how to prevent it
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