Time Capsule takes forever in "preparing backup…" mode

Not sure how long "forever" might be, but it will probably be longer than you might think.

Anytime that you turn Time Machine off, it must take a very deep and very long look at all of your old backups before a new backup will begin. I've seen "Preparing" appear for 6-8 hours or more before an actual backup will begin. The longer your backup history, the longer "Preparing" is going to prepare before the backup begins.

Unless you want to start all over with your backups by erasing the Time Capsule disk, my advice would be to let "Preparing" run until the backup completes......or.....until you see an error message appear. No need to stand watch over the process......check back from time to time maybe every 4 hours.

It would not hurt to restart your Mac again before you attempt to run another backup if possible.

If an error message does appear after a time, please post back with the exact text that you see.

I did turn Time Machine off several days ago (1st time in 10 years) and turned it on today to have a fresh back up before the upgrade.

Turning off the backup is not a good idea.

You are not actually creating a fresh backup. When you turn it back on Time Machine will simply do a major check of every file vs what is in the backup. In a way this is good thing.. but as Bob indicated, if you have a slow wireless link it is very slow and inefficient.

The best way to prepare for an upgrade is to create a bootable clone on a USB drive. On a really old Mac like yours a FW800 drive would be even better. I forget if you have USB3 ports but USB2 are a fair bit slower than FW800.

I recommend you download Carbon Copy Cloner. It is free to use for a month.

Create a bootable clone to USB drive of equal size or bigger than one in the Mac. And then do actually boot from it. The big advantage of a clone is you can check everything is there.. your music, your emails, your documents. Test all your websites and their passwords are working. It should work exactly as your internal drive.. except it will be a fair bit slower of course.

Then you can run the update knowing if anything goes wrong you can instantly recover.

Time Machine is just not as easy or reliable if you need to do a full recover. And it often forgets to save stuff..

Glad that you got things working again!

Any luck?

I have used CCC for many years with flawless results, so I'm with LaPastenague on his recommendation of that product.