Question :

While doing a regular check on my Mac with Disk Utility, it just informed me that I have a potential hardware failure, should save a many data as I can and reinstall.

So I was planning on doing a TimeMachine-backup and disk-reformat, followed by a clean install of OSX and copy-back from TimeMachine.

But… I recently found reports on a bug in TimeMachine, that might prevent TimeMachine from recognizing the latest backup…

Is there a way to make sure that my latest TimeMachine-backup is useable ?

Answer :

This bug seems to occur with unfinished TimeMachine-backups, either due to disconnection, unplugging or switching from WiFi to Ethernet or vice-versa…

As with all things in life, nothing is 100% sure or secure…

But if you want near-100% assurance that your latest TimeMachine-backup will work after a ‘clean install’, do this :

– make sure your Mac is connected to your TimeMachine-backup-disk in only one way, so if it’s an external harddisk disconnect the Ethernet-network cable and set AirPort/Wifi to OFF, to have the connection ‘only via USB’ or ‘only via FireWire’ and if your TimeMachine-backup-disk is a NAS or TimeCapsule, disconnect from AirPort/WiFi (and preferably connect the Ethernet-cable from the NAS or TimeCapsule straight into your Mac, and if possible, stop all other network-connections over Ethernet, by disconnecting all cables, and shutting down AirPort/WiFi) to have the connection ‘only via Ethernet’

– do a new “Back Up Now” in TimeMachine, and make sure it finishes completely before you do anything else (preferably, shut down all other apps before backing up also)

– then startup the Migration Assistant-app (from the Utilities folder in the Applications folder), and type your Mac’s administrator-password when asked

– in the first window, select “From a Mac, Time Machine Backup or startup disk”, and click “Continue”

– in the next window, select the disk that your TimeMachine-backups are on (if you’re on a Time Capsule, you will need to type your TimeCapsule-password when asked), and click “Continue”

– in the next window, a list of all backups (a.k.a. sparsebundles) available on the disk will be displayed ; now you will have to wait a little for each sparsebundle to display what the date is of the backup-version that can be retrieved… if that date matches today’s date, you have a perfect backup available, and you can exit the Migration Assistant-app by repeatedly clicking the “Back”-button

…but if the date is different, or the “No Volumes Found in backup”-error is displayed, your backup is useless for easy recovery ; you will have to exit the Migration Assistant-app, and start over the entire backup-routine explained above, and then check again in the Migration Assistant-app …you have to keep repeating this entire routine until you get today’s date displayed below the backup’s name

If you do not do as described above, you are in serious, enormously time-consuming trouble…  (even though this doesn’t always mean that your personal data is lost… everything might be lost, but… it could also mean you will have to repair the sparsebundle-files and/or it could also mean that you will have to copy everything back ; folder-by-folder or even file-by-file… either in the Time Machine-app or in the Finder ; and all applications will have to be manually reinstalled again…)