Time Machine couldn’t complete the backup on several occasions

Hi MH711,

We understand that you're experiencing some issues backing up your iMac with Time Machine, and we'd like to help any way we can.

You mentioned that the backup fails; when this happens, do you receive a specific error message? If so, what does the error message say?

What type of disks are you using with Time Machine? This page has some great information about the types of disks you can use with Time Machine: Types of disks you can use with Time Machine on Mac

This page also has some great information on how to troubleshoot issues with Time Machine: Time Machine troubleshooting on Mac

Thanks!

MH711 wrote:

I'm running Big Sur on a 2015 iMac retina. I have two external hard drives because eventually one will not backup anymore. Each time it fails to backup I need to erase it and start over, which takes several hours for the first backup. Eventually the other one will fail as well which then requires starting over. Sometimes they both fail at the same time which leaves me in a bind. These failures are unpredictable and sometime happens within a month of initial backup. How can I fix this?

Typically this is an indication the drive is working in a state of failure. Replace it.

MH711 wrote:

This is what I thought when the original drive started failing. I replaced it with a new drive a couple months ago and it failed as well. I'm running two in case one fails but it seems like both fail together after restarting my computer. Just want to make sure getting a new drive will fix this issue so that I don't waste too much money buying drives.

Maybe avoid Western Digital.