macOS Spotlight Indexing Hangs at 0% After Enabling Time Machine Backups to SMB Share

Environment

macOS 13.6 MacBook Pro (Apple Silicon) using Time Machine to a Synology SMB share (SMB protocol, SMB3 negotiated). User enabled 'Back Up Automatically' and also added the SMB mount point to Spotlight indexing in System Settings. Local disk is APFS with lots of small developer files (~200k).

Symptoms

Spotlight indexing progress in System Settings shows 'Indexing: 0% (Preparing)' indefinitely (multiple hours). mdutil reports indexing is enabled for local volumes but returns inconsistent status for SMB share. System search (Cmd+Space) returns incomplete results and Finder searches for file contents return none. Time Machine backups appear to start but report 'Preparing backup' for long intervals.

Observations

Console logs include repeated Spotlight errors: 'mds encountered an error while indexing volume' and 'kMDItemFSNameProbeFor… returned -36' for items on the SMB-mounted Time Machine share. When the SMB share is unmounted, Spotlight switches to 'Indexing paused' and local indexing proceeds slowly. CPU usage for mds_stores is low; network activity to NAS is intermittent—bursts followed by idles. SMB mount uses credentials stored in Keychain; ACLs on share are read/write for the user.

Already attempted

Restarted macOS, unmounted/remounted SMB share, removed and re-added the SMB path from Spotlight preferences, ran sudo mdutil -E to erase and rebuild index for local volumes, and temporarily disabled Time Machine. None produced consistent successful indexing of the SMB path. Did not delete Spotlight database files manually.

Question

Why does enabling Time Machine to an SMB destination cause Spotlight to hang at 0% indexing, and what reversible steps can I take to restore Spotlight and Time Machine to usable state without risking backups or user data?

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AI DIAGNOSTICS

Incident analysis

Updated 1w ago• Trouble ID

Most likely causes

SMB share exposes attributes or file system features (e.g., resource forks, Finder metadata, incompatible POSIX ACL handling) that break mds's file probing routines. 90%

Network instability or SMB signing/encryption settings cause intermittent I/O errors that make mds treat the share as unreliable and stall indexing. 75%

Time Machine sparsebundle creation or locking is interfering with Spotlight's ability to traverse the share, causing repeated probe failures. 60%

Summary

Spotlight errors referencing file-probing failures and -36 I/O errors point to SMB-specific file metadata or permission semantics that mds cannot handle on the remote share, causing indexing to stall. Time Machine over SMB relies on specific server-side support (sparsebundle, proper SMB attributes); if the NAS exposes files with unusual attributes or inconsistent RFC-compliant behavior, mds may block. Safest recovery is to isolate indexing from backup share and verify SMB share compatibility.

Suggested Fixes

Diagnostic step 1

Temporarily remove the SMB Time Machine target from Spotlight indexing: open System Settings > Siri & Spotlight > Privacy (or use mdutil -i off <mountpoint>) so the SMB mount is excluded while monitoring whether local indexing resumes. This is reversible.

Diagnostic step 2

Check NAS SMB settings: ensure SMB3 is enforced, disable SMB signing temporarily for a test if supported (note security implications), and confirm Synology recommended Time Machine/Apple-specific settings are applied. Coordinate with NAS admin and revert after test.

Diagnostic step 3

Validate the sparsebundle on the NAS for Time Machine integrity using DSM's built-in tools (do not delete the bundle). Create a small test SMB share and attempt indexing against it to isolate NAS configuration vs client issues.