Symptoms
Two-way sync duplicates files with names that differ by case between systems.
Use the following observations to establish that this is the specific failure described here, rather than an unrelated outage or different account:
- Failing behavior: Two-way sync duplicates files with names that differ by case between systems.
- Comparison to run: Compare case sensitivity of both filesystems on a test folder.
- Pass condition: Test files sync once without merging two different original files.
Why It Happens
Shares, backup jobs and replication paths each have their own permissions, destination rules and histories; a successful connection is not proof of complete content.
Treat these as competing hypotheses, not confirmed diagnoses. Their implications are different:
- Source and target have different case rules — investigate this first only if the local state or controlled comparison supports it.
- Sync engine resolves rename as conflict — a second layer that may survive a simple restart and requires a targeted check.
- Two clients edit same logical filename — investigate when the first two paths do not account for the observed behavior.
Before Making Changes
Do not apply automatic conflict deletion across production directories. NAS interfaces may report job-level success while individual file operations, permissions, path mapping or remote copies still differ. Verify at the file level and distinguish the original from a restored copy. Write down the working configuration and, if available, export settings or create a test-only copy before changing account permissions, routes or file locations.
Make one change at a time, note the original value, and repeat the exact same test after each change. If the new outcome is worse, restore that single setting; a full reset would erase evidence and can create additional problems.
Problem-Specific Diagnosis
Begin with this controlled observation: Compare case sensitivity of both filesystems on a test folder. Record the result and time; a vague report such as “sometimes fails” cannot distinguish the three hypotheses.
| Check | What to do | What the result tells you |
|---|---|---|
| Compare a working path | Compare case sensitivity of both filesystems on a test folder. | If one controlled route works, the failed route is probably specific to a setting, permission, device, or service rather than a total outage. |
| Check the local state | Pause only the conflicting sync task and preserve both versions. | This can expose or rule out source and target have different case rules without changing several settings together. |
| Inspect the deeper layer | Review conflict-resolution and case-folding behavior in sync logs. | Use the evidence to separate sync engine resolves rename as conflict from two clients edit same logical filename; do not assume either is proven. |
If the local comparison is inconclusive, keep the current system unchanged while checking whether sync engine resolves rename as conflict is consistent with the evidence. If not, investigate two clients edit same logical filename rather than applying every possible fix.
Use Beginner for reversible checks; use Advanced only when the comparison indicates a deeper fault. Two-way sync duplicates files with names that differ by case between systems. Run a harmless test and write down the time, device/account, current status indicators and the exact difference from normal behavior. Compare case sensitivity of both filesystems on a test folder. Do not erase logs or reset the device yet. Pause only the conflicting sync task and preserve both versions. Confirm the relevant account, cable, selected output, permission or status before saving changes. If it is already correct, leave it alone and proceed; do not force a change just to try something. Rename test files to unambiguous names after recording originals. Change only this one condition after recording the old value. If it does not improve the result, restore the former value rather than layering additional guesses on top. Test files sync once without merging two different original files. Repeat the same comparison used in step one. Record what improved, what remains unchanged and whether a reconnect or normal app restart changes the result. Stop here if the expected outcome is stable. Consider source and target have different case rules, sync engine resolves rename as conflict and two clients edit same logical filename separately. Compare evidence from the working and failing paths, and avoid interpreting a green status indicator as end-to-end proof. Compare case sensitivity of both filesystems on a test folder. Review conflict-resolution and case-folding behavior in sync logs. Focus on logs, state, permissions, protocol negotiation or version support relevant to this failure. Do not collect or share credentials, account tokens or unrelated private content. Test one-way sync in an isolated folder before re-enabling bidirectional changes. Use an isolated or test-only configuration where possible. Keep an explicit rollback path; do not weaken security, replace backup originals or bypass equipment protection to make one test pass. Test files sync once without merging two different original files. Observe the behavior through the original trigger again. If the change does not produce this measurable result, undo that change and escalate with the recorded facts, rather than repeating disruptive reset attempts.Step-by-Step Troubleshooting
Capture the failing state
Check the first reversible condition
Apply the lowest-risk targeted fix
Retest and document
Distinguish the competing root causes
Inspect the deeper system layer
Run a second independent isolation test
Validate stability and rollback readiness
Solution Checklist
Common Mistakes to Avoid
- Treating source and target have different case rules as certain before running the comparison: Compare case sensitivity of both filesystems on a test folder.
- Trying several changes at once, such as modifying sync engine resolves rename as conflict and two clients edit same logical filename simultaneously, which makes the successful change impossible to identify.
- Ignoring the safety boundary: Do not apply automatic conflict deletion across production directories.
- Assuming that a status label or progress indicator guarantees the actual action completed; verify the outcome independently.
How to Verify the Fix
Test files sync once without merging two different original files.
- Repeat the original failing action under equivalent conditions: Two-way sync duplicates files with names that differ by case between systems.
- Run the control again: Compare case sensitivity of both filesystems on a test folder.
- Check the positive pass condition: Test files sync once without merging two different original files.
- Recheck after a normal restart, reconnection or scheduled cycle only when it is safe and relevant.
A single passing attempt is useful but may conceal intermittent failures. Record whether the fix survives the triggering condition without requiring a daily workaround.
If the Problem Continues
Use the deeper comparison rather than repeating the first steps: Review conflict-resolution and case-folding behavior in sync logs. Test one-way sync in an isolated folder before re-enabling bidirectional changes.
Collect job ID, anonymized path, protocol, client version and relevant error excerpts without uploading private file contents or exposing NAS management to the public internet.
If the issue affects money, alarms, shared business records, or protective power equipment, stop risky experiments and use the official administrator, provider or manufacturer channel.
Prevent Recurrence
- Keep a record of the previously failing condition: Compare case sensitivity of both filesystems on a test folder.
- Preserve the corrected behavior: Test files sync once without merging two different original files.
- Keep tested offline or immutable copies of critical data, record job exclusions, and periodically restore a small sample into a separate test location.
- Review configuration or hardware changes that could reintroduce source and target have different case rules.
Frequently Asked Questions
Does this symptom prove source and target have different case rules?
No. Start with the controlled comparison: Compare case sensitivity of both filesystems on a test folder. Only treat source and target have different case rules as a candidate until the evidence supports it.
What if the first two checks do not change anything?
Move to a different layer rather than repeating the same action: Review conflict-resolution and case-folding behavior in sync logs. That helps determine whether sync engine resolves rename as conflict or two clients edit same logical filename fits the symptoms.
How do I know the repair actually worked?
Use this outcome, not just an on-screen status message: Test files sync once without merging two different original files. Keep a record of the working state for future troubleshooting.