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Reply To: [Solved] iMac 24″ M3 Time Machine Backup Hanging on ‘Preparing Backup’ (macOS Sequoia 15.1) – Verified Troubleshooting
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November 15, 2026 at 5:05 am
#20076
Mark Mason Senior Specialist (Lvl 8)
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:
- Stop backup daemon:
sudo tmutil stopbackup && sudo killall -9 backupd. - Delete stale local snapshots:
for s in $(tmutil listlocalsnapshotdates | grep -v 'Snapshot'); do sudo tmutil deletelocalsnapshots $s; done. - 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 14″ M4 Pro (48GB) | iPhone 15 Pro | iPad Air M2 | Milan, IT
Apple Certified Support Professional (ACSP) | iOS / Swift Engineer