Time Machine Backup Stuck after preparing

Thanks BDAqua. I ran Disk Utilities First Aid (DUFA) on one of my backup disks and that appears to have addressed the issue. It took overnight for it to run which is why I didn't report back yesterday. I had automatic backups turned on which meant it ran the backup after DUFA finished. The backup was successful and completed after DUFA. I ran the backup again and it only took a few minutes at most. I will run it on the other disk as well and see how it goes.

I will also look into Drive DX as that sounds interesting and I prefer know more about the health of the disk which DU doesn't really provide.

I am surprised this issue hit both disks at the same time.

Thanks for your help, it is appreciated!

This appears to have resolved the issue with the second disk as well, which is great! It took a day for DUFA to run and unfortunately my latop got into a state where it wouldn't let me get out of the screen saver (finger print didn't work and it wouldn't show me the password field); the entire screen was red and I could move the mouse around. I didn't want to reboot since I could hear the disk going while DUFA was running. This morning the disk was quiet so I was able to reboot and things appear to be ok.

The remaining question I have is, will DUFA take about 24 hours to run every time I run on these backup disks, or was that a one time thing because I had not previously run it (or it has been a long while) ?

The drives I am using have roughly 3.75 and 4.4 TB remaining each. The laptop is a 2 TB drive and most changes do not occur there at this point. I take a lot of photos so I am eating some space but the external drives have been more than adequate.

Both external drives took a long time when running DUFA, so it isn't an isolated incident.

W.r.t. the boot drive (the laptop), how would that affect the DUFA running on the external (non-boot drives) ?

W.r.t. Drive DX, I don't own it yet, but was planning on getting it and running it. My machine was tied up for a couple of days running the above.

Also, I forgot to mention, I have Sophos running, I don't know if this would impact DU.