Mac can't backup to its own TM drive ... ?

[RedTomato]

This is a crazy one.

I have a mothership mac on Mojave, with various drives attached. I'm using one HDD as a shared Time Machine drive, and various other household macs are backing up to it, no problem. I decided to use that TM drive to back up the mothership mac too. Selecting it in TM Preferences got this:

"The disk must be erased before it can be used for Time Machine backups because it has an incompatible filesystem. Erasing will destroy all information on the disk and can't be undone."

WTF? I checked the HDD in Disk Utility, and sure enough, it's formatted in APFS. (I must have done this as an experiment when APFS came out months ago) Every single other mac in the house is able to back up to it, including a 10 year old white MacBook running an ancient version of OSX, but the actual mac it's attached to can't use it!

Insanity abounds!

 

[fisherking]

perhaps the issue is right in front of you; that you have backups on older OSes... maybe a problem for the newer OS. how many macs use this for TM? and what OSes are they running?

 

[LuisN]

perhaps the issue is right in front of you; that you have backups on older OSes... maybe a problem for the newer OS. how many macs use this for TM? and what OSes are they running?

Time Machine local drives must be formatted to HFS. Remote machines do backup because they see a network file system, it could even be formatted as NTFS or EXT4 file systems as long as they are shared over a network

 

[RedTomato]

perhaps the issue is right in front of you; that you have backups on older OSes... maybe a problem for the newer OS. how many macs use this for TM? and what OSes are they running?

It's nothing to do with the older OS. The below poster is correct.
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Time Machine local drives must be formatted to HFS. Remote machines do backup because they see a network file system, it could even be formatted as NTFS or EXT4 file systems as long as they are shared over a network

Indeed you are correct. This means that every other mac in my house can back up to the drive except the actual mac it's attached to.

As I said, madness!