I turned on my iMac today and suddenly, my WD external hard drive has gone read only. It's been making Time Machine back-ups for years, and today, it just stopped working.
I've confirmed I have read and write access (right-click on the drive), although in Disk Utility it says Users Disabled. I have even reformatted the drive.
What now? Why is this even happening?
iMac 21.5″ 4K, macOS 13.7
Time Machine backup drives are now by default normally read-only status since APFS became the normal format for these drives with macOS 13 Ventura.
Time Machine wants to own the backup drive.
If TM has stopped making backups, you should check the free space on the backup drive. Although TM is suppose to delete older backups to free up space, this process often doesn't seem to work to our satisfaction. If the free space on either the backup drive or the startups drive gets too low, TM may have trouble completing its backups.
A couple options are 1) erase the drive and start a fresh backup or 2) get another external drive and start a fresh backup on that while putting the current drive away for archive or erase it and use it for additional storage.
How much free space do you have on your iMac's boot drive?
It must have enough room for a local snapshot by TM.
If you launch Disk Utility and have Show All Devices checked in DU's View menu you'll see any local snapshots at the bottom of the window:
If you don't have enough free space for a local snapshot on the boot drive TM will not backup.
+1
WD external hard drive has switched to read only
