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[Solved] Mac Studio M2 Ultra encountering Time Machine Backup Hanging on ‘Preparing Backup’ after update (macOS Sequoia 15.1)

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Home › Forums › MacBook, iMac & macOS Lab › [Solved] Mac Studio M2 Ultra encountering Time Machine Backup Hanging on ‘Preparing Backup’ after update (macOS Sequoia 15.1)

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  • November 14, 2026 at 10:06 pm #13111
    Willie Ramirez
    Community Contributor
    Diagnostic Hardware Specs: Mac Studio M2 Ultra | OS Version: macOS Sequoia 15.1 | Archive Source: Apple Support Community #256534238

    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 Pro 14″ M4 Pro (48GB) | iPhone 15 Pro | iPad Air M2 | Bristol, UK
    iOS / Swift Engineer | "Verified Apple Discussions Archive"
    November 14, 2026 at 10:06 pm #13112
    Stella Murphy
    Certified Tech (Lvl 5)
    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.

    MacBook Pro 16″ M3 Max (48GB) | RME Babyface Pro FS | Genelec 8330A | London, UK
    Apple Certified Support Professional (ACSP) | Logic Pro Audio Producer & Mixing Engineer
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