time machine

I have a Verizon Fios modem that’s doing 300 mbps

The Fios is a router.. if you are running it as a router then you can attempt to fix up the setup.. but if the TC is earlier than Gen4 which is A1409 I mentioned I think it has reached 6-8 years old and is time to pension off unless you are prepared to do considerable work on it.

If you want a network backup then TC can still be used but you need to reconfigure the TC.. do a full erase as Bob suggested.. even a low level format to ensure the disk is still good.. and start over. Happy to help with that if you wish to try but it might really be time to move on.

My time machine erases old backups and restarts on its own. Extremely slowly.

Does this occur every time that you try to run a backup? If not, how often does this occur?

Please be aware that Time Machine has not been all that reliable since Sierra was introduced. The problems have continued with High Sierra and Mojave as well. Does the screenshot below look familiar?

Good plan to use Carbon Copy Cloner. Not sure how much time that you want to spend to try to get Time Machine running.

If you want to try to use Time Machine, you will need to manually erase the Time Capsule drive and then start over again. Do not trust Time Machine to delete your old backups, erase the drive yourself using AirPort Utility.

No guarantees that this will help for you, but this has helped here. On average, I see the dreaded message about every 3-4 months or so.

FWIW, I use CCC in addition to Time Machine. I have gone through the process of accessing CCC backup to gain access to individual files and have found it to be a straight-forward process without any issues.

In addition, I "solved" my TM issues, by not relying on a Time Capsule. Instead, I use TM with both an externally attached drive (WD My Book Pro) and with my Synology NAS. I've yet to see that "error message" that Bob provided, using these devices.

I have an ancient Time Capsule Version 7.6.9.

My Time Capsule communicates with my iMac via WiFi

The combo of very old TC and using wifi is not good. Wifi on the old TC is very slow.. are you using a different wireless router in the mix?

Corruption of backups over the network is very noticeable problem. Especially since Sierra.

Could you move the TC closer to the computer and use ethernet? Is the TC doing something other than running TM backups in the network?

Tell us a bit more about your whole network layout.

What modem do you have? Make and model. Is it also a router?

What model TC? Please give us the A1xxx model from the base.. e.g. A1409 is Gen4.

How is the TC configured?

Check your actual wireless link speed by holding down the option key and clicking the wireless fan. If you have a slow connection that will tend to make corruption far more likely.

For a desktop Mac it is much more reliable to use a local drive like a USB plugged into the Mac directly.

Another +1 for CCC and like Tesserax I run TM as well but trust ONLY CCC.

In fact I reached the point where TM became the secondary backup and CCC is the more important.

... and what have you tried, so far, to resolve this yourself? Which exact model is your Time Capsule? ... or are you using Time Machine to back up to drive directly connected to your iMac?