Why does Time Machine fail to backup

after the iMac has been turned off and back on? The message I receive is more or less "Time Machine failed because the HDD is read only".

Simple question I can't find the answer to. Or am I seriously meant to leave the iMac on 24/7?

As a matter of interest, how do you get it to work again?

This is not typical behaviour and may indicate a fault with the backup disk. The first step would be to run "repair permissions" on it. You may want to check this article: https://www.lifewire.com/fix-time-machine-errors-225...

Agree with Tiny - I'd suspect a faulty HDD. Run Disk Utilities over it as a first step.

Remove drive from USB Cable (its already been uncounted), then reconnect to usb cable then use Time Machine Preferences to allocate the drive.

I have run repair permissions and it finds nothing. Everything is fine if I leave the iMac on, it just seems after I have rebooted this problem occurs.

Did you run Disk First Aid in Disk Utilities?

Yes I have

However I have noted that the MAC HDD is APFS and the backup is MacOS Extended (Journalised) - could that be the problem?

Nope.

What did Disk Utility say about the Ext HDD?

that its perfect.

Mind you, I have realised what caused the problem (well it seems ok at the mo). The WD driver software was missing, I've downloaded it and had two successful shut downs without Time Machine throwing the failed error.

Urgh.

Failed again after reboot

Files can�t be copied onto the backup disk because it is read-only. You may need to repair or erase the disk using Disk Utility. If the disk can�t be repaired, select a different disk for backups.

Immediately, I used First Aid to check both the volume Time Machine and the actual drive. Both said no problems.

Going to leave the imac on and will see if backup fails again.

Edited by blfamily (Tue 21-May-19 06:58:02)

I'd be inclined to try a different backup drive. That would help to pinpoint whether the problem is with the drive or the computer.

External drives shouldn't require any drivers for normal operation.