What does Windows error code 6849 (ERROR_BAD_CLUSTERS) mean?

 
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ERROR_CANNOT_ABORT_TRANSACTIONS ERROR_COMPRESSION_NOT_ALLOWED_IN_TRANSACTION

ERROR_BAD_CLUSTERS

The operation could not be completed due to bad clusters on disk.

ERROR_BAD_CLUSTERS is Win32 error 6849 (0x00001AC1) and concerns an operation blocked by bad disk clusters.

Where the result appears

  • reading or moving a file whose extents intersect damaged sectors.
  • running volume maintenance.
  • extending a file on degraded media.
  • repairing a volume after hardware errors.

What to verify

Verify whether all physical clusters required by the file or volume can be read, remapped, or replaced without losing required data. Check physical disk and volume identity, failing logical offsets or cluster numbers, and SMART, controller, and System log events.

Likely causes

  • the device reported uncorrectable sectors.
  • previously marked bad clusters contain required data.
  • media degradation exceeded controller recovery.
  • a virtual disk or storage path returned persistent read errors.
  • the file system cannot relocate data from a damaged extent.

Troubleshooting steps

  1. Collect physical disk and volume identity.
  2. Record failing logical offsets or cluster numbers.
  3. Correlate SMART, controller, and System log events with the Windows System log, NTFS/ReFS events, storage-controller diagnostics, application integrity checks, and backup or replica logs.

Handling, retry, and recovery

Stop unnecessary writes, copy recoverable data, run the supported volume and hardware diagnostics, replace failing media, and restore any unrecoverable files from backup.

Related errors

ERROR_VOLUME_DIRTY signals that consistency checking is required; this code identifies clusters already known to be physically or persistently unreadable.

Example

A backup job repeatedly fails at the same file offset. Disk diagnostics confirm an uncorrectable sector, so the volume is evacuated and the file is restored from another replica.

Developer and administrator guidance

Administrators should prioritize data preservation and hardware evidence before repair. Developers should separate structural file-system success from application-level integrity, because a readable or repaired file can still be semantically incomplete.

References

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