Check File Sync progress inside a failed session

Source facts

A File Sync session can fail overall or report per-item errors while still synchronizing some files. Microsoft identifies the Applied fields as evidence of how much succeeded, rather than treating the aggregate result as a complete description.

Event 9121 is recorded for each per-item error after the session finishes and provides persistent and transient counts. Microsoft specifically advises investigating persistent per-item errors. Microsoft Learn.

Applicability

Identify the affected server endpoint, session interval, and files whose availability matters. Keep overall session status, observed progress, and unresolved item failures separate in the incident record.

DSE recommendation

DSE recommends comparing consecutive session evidence before choosing the next action. Record which applied counts are changing and which item errors persist. Ask the file-service owner to prioritize unresolved business-critical files rather than dismissing the incident because other files made progress. Avoid restarting or rebuilding the endpoint solely from the aggregate failure label.

Verification

For an approved sample, reconcile applied-file evidence with the destination and inspect the corresponding per-item events. Confirm whether the next session advances and whether the same items remain blocked. Preserve endpoint identity, session timestamps, relevant counters, and sanitized error details so another operator can reproduce the diagnosis.

Official references

Microsoft Learn: Monitor Azure File Sync. Source retrieved September 9, 2026.