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The Apple Support Community will permanently close on November 20, 2026. Starting today, the site will no longer accept new posts and is available in a read-only state.
You can continue to find trusted guidance and support on the official Apple Support site.
We want to thank the community members who have contributed their time and expertise to help others with their Apple products.
Unable to mount the volume the external hard drive on the Mac after Catalina upgrade.
Getting the error below:
Any idea so that I can access the content of the volume?
iMac Line (2012 and Later)
That external drive is formatted for PCs:
Unless you're going to share the drive with a PC you should format it as OS X Extended (journaled) with ownership set to be ignored.
Downgrade the Mac to 10.10.5 and after some time, the external hard drive finally mounted by itself.
Now the issue is unable to open the photos library stored on the external hard drive.
I created a partition on Mac hd and called it Mac hd2, installing Catalina on it and will see what happens.
Please see the formatting on the screenshots below:
I have the same issue too. Its an Synology NAS and there I have old TimeMachine BackUps. But since I use Catalina, the images can't be activate by DiskImageMounter. The HD is GUID formatted. Can anyone help? All other documents on the NAS I can read or write new one. I only have the problems with my old TimeMachine BackUps.
Do you know how the drive was formatted?
Mac os. I use a WD my book(8T) as an external hard drive for time machine, and mac can't mount the drive.
Time Machine was able to use the drive before you upgraded to Catalina?
How is it formatted and connected to your Mac?
Does the drive meet these specifications: Backup disks you can use with Time Machine - Apple Support.
com.apple.DiskManagement.disenter error when mounting external hard drive
