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Reply To: [Solved] How to fix Time Machine Backup Hanging on ‘Preparing Backup’ caused by APFS snapshot journal comparison deadlock over SMB network share on iMac 24″ M3
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Claire BennettPruning 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.