X_STORAGE_WRITE_OUTCOME_UNKNOWN
Means
a write was sent and its answer lost, and the disk could not say whether it landed
Typical cause
the connection died after the last request of a write was sent and before the provider answered, and neither a stat of the key nor an abort of the upload could settle whether the object is the one sent
Fix
await disk.stat(key) — the size and etag now at the key; the same as what was sent means it landed