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On-callMedium
Question
An upload-processing service starts failing with 'No space left on device' when writing temp files, but `df -h` shows the data volume is only 47% full. Writes are erroring across the whole fleet on the same mount. `df -i` shows inode usage at 100%. The directory that holds per-job scratch files has tens of millions of tiny files, and a cleanup cron that used to delete finished jobs' scratch dirs was disabled in a refactor two weeks ago. How do you triage this confusing 'disk full but not full' symptom and recover?
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
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