Seagate Backup Plus Drive

This would indicate that your drive is partitioned, meaning it has multiple volumes on one physical disk. You should check both volumes, and see if there is data on them you need. They appear as separate "disks" on your desktop. Once you are backed up, or don't need the data, you should try to erase the entire disk.

1. Go to Disk utility. You can click on Finder > Go > Utilities > Disk Utility
2. Click View, and click "Show All Devices".
3. Click the highest, and non indented, drive. (The name should end in Media).
4. Select the Erase button, and use Mac OS Extended (Journaled) and GUID Partition Map. You can call it whatever you want.
5. This should erase the entire drive. You can try Time Machine again.

Below is a visual component of a generic Disk Utility disk and the top drive there.

Hi krystyna144,

Welcome to Apple Support Communities. Do you need the data from this drive? If not, it is probably best to erase it and start fresh for the new Mac. Erasing will delete everything on it!

If you need the data, attempt to copy and paste the data to your iMac. You can also try First Aid before erasing it to repair it Repair a storage device in Disk Utility on Mac - Apple Support

Erase a Time Machine Drive:

1. Go to Disk utility. You can click on Finder > Go > Utilities > Disk Utility
2. In the toolbar, click View, and click "Show All Devices"
3. Select the Seagate external Hard Drive name, the top name listed. It will be in the "external" section of Disk Utility.
4. Click Erase, Use Mac OS Extended (Journaled) and GUID Partition Map. You can call it whatever you want.
5. Click Erase

You can now set it up as a Time Machine Drive:

1. Go to System Preferences
2. Go to Time Machine Settings
3. Click "Select Backup Disk."
4. Select the disk you just erased and created.

This should get you on your way to backing up again!

Cheers,

Jack

Hi again,

That is quite odd. Try these steps:

1. If the drive appears on your desktop, drag it to the trash to eject.
2. Keep it unplugged while you restart your Mac.
3. Once your Mac is on, and you're logged in, plug the drive back in.
4. Try to setup Time Machine again.

If it still does not work, go to Disk Utility again, click View, and click "Show All Devices." Click the name(s) for the Seagate drive. Then click "mount" in the top toolbar for each.

See if this works!

Cheers,

Jack