Why Sequoia corrupts Time Machine backups
Short answer: macOS Sequoia (15.x) changed how Time Machine stores and verifies APFS snapshots (point-in-time copies of your filesystem). Backups created under Ventura or Sonoma used an older band-file layout inside the sparsebundle (the single large file that contains all Time Machine backups for one Mac). When Sequoia first runs a backup on the old sparsebundle, it performs a full re-catalogue. If this re-catalogue is interrupted — by a power cut, a loose cable, or a Wi-Fi drop on a network drive — the sparsebundle header is left in an inconsistent state, and Sequoia refuses to use it thereafter. Indian homes and offices with unstable power are disproportionately affected.
How to recover your Time Machine data under Sequoia
Step 1: Check local APFS snapshots first
Before touching the external Time Machine drive, check whether your Mac’s internal SSD has usable local snapshots. macOS creates hourly local snapshots automatically, stored on the internal APFS volume. Open Terminal and run: tmutil listlocalsnapshots /. This lists all local snapshots by date (format: com.apple.TimeMachine.YYYY-MM-DD-HHmmss.local). If you see snapshots from the last few days, run tmutil restore -s [snapshot-name] /path/to/file /Volumes/Recovery/restored-file to extract individual files. For a full system restore from a local snapshot, boot into macOS Recovery (hold Power on M-series, or Command+R on Intel), choose Restore from Time Machine Backup, and select the local snapshot. This works even with a corrupted external drive.
Step 2: Mount the sparsebundle read-only
If local snapshots do not have the files you need, attempt to manually mount the sparsebundle from the external drive. Plug in the drive, then open Terminal and run: hdiutil attach -readonly /Volumes/[DriveName]/[YourMacName].sparsebundle. The -readonly flag prevents any writes to the bundle during mounting, which is critical — attempting to “repair” a corrupted bundle by mounting it read-write often destroys remaining data. If the command succeeds, a volume named “Time Machine Backups” will appear in Finder. Browse to /Backups.backupdb/[YourMacName]/ and manually copy files you need. Copy your most critical files first — the mount may be unstable.
Step 3: Use tmutil to list and access snapshots inside the bundle
If hdiutil mounts the bundle but the folder structure looks empty or partial, the APFS snapshot catalogue inside the bundle may be intact even if the outer directory is damaged. Run tmutil listbackups with the bundle mounted to list individual backup dates. Then use tmutil restore to pull specific files from specific dates: tmutil restore "/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/[Mac]/[Date]/[Volume]/path/to/file" ~/Desktop/recovered/. This gives you granular access to files from specific points in time, bypassing the need for the bundle’s outer catalogue to be intact. For a related recovery scenario, see our APFS snapshot recovery guide for accidental deletes.
Step 4: The India angle — power interruption is the main cause
The most common trigger we hear about from Indian Mac users is a power cut during a macOS Sequoia upgrade or the first backup after upgrading. Sequoia’s initial backup run can take 3–6 hours on a well-used Mac. A power cut at any point during this window can corrupt the sparsebundle header. The fix: always upgrade macOS on AC power with a UPS, or ensure the Mac is on battery (a fully charged MacBook battery will last well past the upgrade). For NAS-based Time Machine backups (common in small offices), ensure the NAS also has UPS protection — a NAS power cut during a backup write is equally destructive. Our data recovery service can help if sparsebundle repair has reached the limits of Terminal commands.