"preparing backup" WD 4TB passport won't backup

Everything in Time machine runs sequentially at low priority in the background. An initial backup can take all afternoon in the "preparing backup" stage -- but you can continue to use your Mac while it is in any stage of backing up.

If you connect your backup drive again soon, such as every-other day, Time machine can use a System Data Structure called the File System Event Store (a circular list of what folders have changed recently) to compute what needs to be backed up very quickly, and will only take a few minutes in the "preparing backup" stage.

If you leave it much longer, the File System Event Store may become stale, and Time machine will have to re-compute 'what needs to be backed up' from scratch, again taking all afternoon.

Hello bkmmtl,

We understand you continue to see "Preparing backup" when your external hard drive is connected to your MacBook Pro. We'd like to help you get this resolved.

Are you seeing that message in Time Machine, or do you see it someplace else? How long does it continue to display that message? There are various factors that can cause it to take longer than expected when backing up using Time Machine. Check out the information about this here: If a Time Machine backup takes longer than you expect.

If you're using Time Machine, you can try stopping the backup, and then restarting it. You can stop the backup by clicking on the little "x" next to it in Time Machine preferences. Before starting the backup again, power your Mac off and back on. Also, make sure your Mac is fully updated: How to update the software on your Mac.

Thanks for using Apple Support Communities.

Take care.