What does Windows error code 6647 (ERROR_LOG_APPENDED_FLUSH_FAILED) mean?

ERROR_LOG_APPENDED_FLUSH_FAILED

Records were appended to the log or reservation changes were made, but the log could not be flushed.

ERROR_LOG_APPENDED_FLUSH_FAILED belongs to Common Log File System (CLFS). A diagnosis of this result must connect the condition to the producing API, current state, object identity, and first lower-level diagnostic.

This result is Win32 error 6647 (0x000019F7) in Common Log File System (CLFS). Interpret it at the call that produced it and use the system message above as the immediate condition rather than as a complete root cause.

Where the result appears

• committing a transaction record.
• changing reserved log space.
• writing a checkpoint that must precede data changes.
• closing a client after appending recovery information.

State boundary to prove

This result applies to a CLFS append or reservation change whose flush failed and does not by itself prove that the entire server, directory, disk, session, or application is unavailable. The state boundary to prove for this Win32 error is whether the newly appended records or reservation update is confirmed durable before dependent work proceeds. Use LSN returned by the append, flush mode and completion status, and dependent data updates already issued as independent evidence. When evidence for this Win32 error disagrees, preserve timestamps and investigate the transition instead of selecting the most convenient value.

Likely causes

• the append reached cache but the durability flush failed.
• the volume became unavailable after the write.
• storage reported a media or controller error.
• a failover interrupted the flush barrier.
• the application continued after a partial append path.

Diagnostic sequence

1. capture error 6647 immediately at the API boundary and record the operation that was attempted.
2. identify the exact owner of a CLFS append or reservation change whose flush failed, including object generation, server, path, session, replica, or client context.
3. collect LSN returned by the append before restarting a service or changing configuration.
4. compare flush mode and completion status with the documented or observed precondition.
5. correlate dependent data updates already issued with the owning application log, CLFS-related System events, storage events, and any transaction or recovery trace.
6. determine whether side effects occurred and verify recovery after changing one responsible condition.

Evidence to collect

• LSN returned by the append.
• flush mode and completion status.
• dependent data updates already issued.
• storage events at the same time.
• result of reopening and locating the record.

Correlate it with the owning application log, CLFS-related System events, storage events, and any transaction or recovery trace. Keep the first detailed status even when a later wrapper translates it to error 6647; the first status often distinguishes transport, authorization, storage, schema, state, and application-integrity causes that share the same final Win32 result.

Handling, retry, and recovery

The recovery objective is to assume commit state is uncertain, prevent dependent irreversible actions, reopen or verify the log, and use the application transaction protocol to decide whether to replay, compensate, or retry.

Retry it only after the recorded condition changes and completion state is known. Idempotent queries may be repeated after recovery, but mutations require a state check first; backoff cannot repair malformed input, corruption, missing structure, or policy rejection.

Telemetry and support fields

• record log_appended_flush_failed_api for the producing function or management operation.
• record log_appended_flush_failed_target for the file, log, session, replica, object, or server identity.
• record log_appended_flush_failed_state_before and log_appended_flush_failed_requested_transition.
• record log_appended_flush_failed_first_status for the earliest lower-level diagnostic.

For support escalation involving it, retain decimal 6647, hexadecimal 0x000019F7, the API, UTC time, target identity, and first subsystem-specific status. Include the smallest reproducible request and evidence that distinguishes this condition from nearby codes. In the context of it, clfs clients can run in user mode or kernel mode, so the same win32 result may be returned through an application wrapper, a service, or a driver-facing management path.

Difference from nearby results

ERROR_LOG_CONTAINER_WRITE_FAILED means the write failed; this code allows that bytes were appended but says durability was not established.

Practical validation scenario

A service receives an LSN for a commit record but the subsequent flush fails. It records the transaction as indeterminate and checks the log after storage recovery instead of issuing the business operation twice. The negative test should preserve the responsible condition and reproduce it; the recovery test should change only the identified cause, repeat the same operation, and verify both success and the absence of an unintended partial side effect.

Developer and administrator guidance

Administrators handling it should preserve the complete CLFS set—base log, containers, security metadata, and application checkpoint state—before repair. Developers should never delete or recreate a container merely because its path appears in the error; the owning recovery protocol determines whether that data is still required. Code that exposes it through RPC, JSON, REST, PowerShell, or another protocol should preserve the Win32 domain, decimal 6647, hexadecimal 0x000019F7, and original component diagnostic.

References

• Microsoft: Win32 system error range containing this code — official context relevant to it.
• Microsoft: Common Log File System — official context relevant to it.
• Microsoft: Creating a Log File — official context relevant to it.
• Microsoft: Introduction to CLFS — official context relevant to it.

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