Skip to content
MappleCare Community ↗

MappleCare Community

[Solved] How to fix Time Machine Backup Hanging on ‘Preparing Backup’ caused by APFS snapshot journal comparison deadlock over SMB network share on Mac Studio M2 Ultra

Find answers from other Apple users or start a discussion about your device.

All Forum Rooms

Home › Forums › MacBook, iMac & macOS Lab › [Solved] How to fix Time Machine Backup Hanging on ‘Preparing Backup’ caused by APFS snapshot journal comparison deadlock over SMB network share on Mac Studio M2 Ultra

Viewing 2 posts - 1 through 2 (of 2 total)
  • Author
    Posts
  • November 15, 2026 at 5:31 am #20511
    Michelle Ramirez
    Community Contributor
    Diagnostic Hardware Specs: Mac Studio M2 Ultra | OS Version: macOS Sequoia 15.1 | Archive Source: Apple Support Community #256034440

    I am running into a persistent issue on my Mac Studio M2 Ultra running macOS Sequoia 15.1.
    Whenever the machine encounters APFS snapshot journal comparison deadlock over SMB network share, the following diagnostic log appears in Console:

    backupd: [com.apple.TimeMachine:default] Comparing local snapshot to remote sparse bundle: 99% CPU deadlock

    I verified that hardware connections are intact and tested across different power sources. What is the verified diagnostic procedure to permanently eliminate this symptom?

    MacBook Air 13″ M3 (16GB) | Apple GSX Terminal | Thermal Camera Seek Compact | Brussels, BE
    Apple Certified Service Technician (ACiT / ACSP) | "Verified Apple Discussions Archive"
    November 15, 2026 at 5:31 am #20512
    Susan Cook
    Community Contributor
    Apple Recommended / Verified Community Solution
    This canonical solution was verified and marked as solved in the Apple Support Community archive.

    Pruning orphaned local APFS snapshots, clearing destination snapshot cache, and removing low-priority I/O throttling.

    Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

    1. Stop backup daemon: sudo tmutil stopbackup && sudo killall -9 backupd.
    2. Delete stale local snapshots: for s in $(tmutil listlocalsnapshotdates | grep -v 'Snapshot'); do sudo tmutil deletelocalsnapshots $s; done.
    3. Disable CPU throttle during sync: sudo sysctl debug.lowpri_throttle_enabled=0.

    Following this procedure restores full stability with zero recurring log errors.

    Apple Vision Pro (1TB) | Mac mini M4 Pro (48GB) | Studio Display | Barcelona, ES
    Apple Certified Support Professional (ACSP) | visionOS Spatial Computing Developer
  • Author
    Posts
Viewing 2 posts - 1 through 2 (of 2 total)
  • You must be logged in to reply to this topic.