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ERROR_LOST_WRITEBEHIND_DATA
What ERROR_LOST_WRITEBEHIND_DATA means
This is a serious data-integrity warning. An application may have completed an earlier write successfully because the data entered a cache, but the later background flush failed. The affected data can be lost even though the original write call reported success.
Where it commonly appears
- Network shares that disconnect after cached writes
- Removable or failing storage
- Write-back caches without reliable power protection
- File systems or drivers that fail during lazy-writer flush
Likely causes
- The device or network path disappeared before flush
- The medium became read-only or full
- A controller, cable, or disk reported an I/O error
- A remote server rejected or lost the delayed write
- A filter driver failed paging or cached I/O
Diagnostic checklist
- Treat the named file and surrounding transaction as potentially inconsistent
- Review System event logs for disk, NTFS, redirector, controller, and network events
- Check free space and storage health on both local and remote systems
- Compare application-level checksums, transaction logs, or replicas
- Preserve the exact time range because the original write may have occurred earlier
Guidance for developers
Do not retry only the final flush and assume the file is correct. Reopen and validate the durable content, then replay from a transaction log or authoritative source. Applications that require durability should use documented flush semantics and still handle device-level failure.
Guidance for administrators
Stabilize the storage path before allowing more writes. On network shares, verify server availability and lease/oplock behavior. On local storage, check controller and disk health and replace unreliable hardware.
Example incident
A service writes a configuration database to a network share. The call returns success, but the link fails before the lazy writer commits the pages. This status appears later. Recovery must validate or restore the database, not merely reconnect the share.
Related conditions
Unlike ERROR_WRITE_FAULT, the failure can be reported after the initiating write. Unlike ERROR_DISK_FULL, the root cause is not necessarily capacity.
Operational decision points
The first production question is whether this event reflects a durability condition and not merely a transient API failure. For ERROR_LOST_WRITEBEHIND_DATA, the deciding evidence is affected path, original write interval, flush result, storage events, checksum. Preserve this first-occurrence evidence before retrying.
- State change required: the next attempt is justified only after the relevant durability state can differ from the failed attempt.
- Escalation evidence: preserve affected path, original write interval, flush result, storage events, checksum together with component version and the first preceding failure.
References
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