Time Machine

I have TWO SSD drives connected to my iMac, and a single NAS drive that contains my Time Machine backups.

One SSD have Mojave, the other Catalina. so I can boot from either one via System Preferences. However, if I boot to Catalina (and I tell it NOT to do TM), when I boot back to Mojave, it asks me if I want to use “Drive X” for TM… where drive X is what it always had been useing… then proceeds to make a BRAND NEW backup, leaving the old one there as well… this obviously takes not only a ton of time, but a ton of space

Any ideas how to force Mojave to stay with on backup image?

Hmm, don’t have an answer why it does that, but you could just disconnect the NAS when booting to Catalina.

thought about that, but the NAS services 4 other computers in my LAN as well

is it shared through your computer to the rest ?

I dont recall having this issue on my old MBP when I’d boot back and forth between Catalina and Mojave BUT I had also explicitly set up Catalina to NOT use time machine when I installed it which you also seem to have done

weird issue

I know going forward Catalina would NOT adopt my old TM backups from Mojave for some reason (not encrypted or something screwy like that)

the NAS is a LAN device… not just a HDD…

Mojave is installed on the internal iMac drive, CAT is on its own SSD connected to the same computer. I cloned the internal to the SSD then installed CAT on it… so when I boot CAT it has the same files etc (for testing)… as such I thought I’d turned off TM there…

Guess later today, I’ll boot CAT and make sure TM is totally disabled, and see what Mojave does then

Ah you did this a little different than I usually do
My Catalina drive was a wiped brand new SSD that I installed onto - clean

Since the machine cross mounts all attache devices there was no need or reason to clone all the files etc there first

yeah most of my stuff is on another SSD, but there are still installed apps on the internal (before I thought to move them) So I kinda wanted to test CAT with the same stuff I use normally.

If/when I decide to move to CAT… I’ll wipe that SSD and start over

ah I just started them off the other drive :stuck_out_tongue:
being lazy you know

I think Time Machine settings are stored in PRAM (or whatever the cool kids call it these days). I’ve seen this before.

This time around, I split the drive into 3, so all my important stuff is on one partition. With Time Machine configured to ONLY backup that partition and not the others. But I will check it next time I run some BS.

if I understand, you’re connecting the NAS using usb to your imac, and using lan to other computers ? I would never mix like this. only lan access for a NAS.
btw catalina does “something” to the time machine backups, and after than older macos can’t use the backup anymore. one customer backup was completely crashed after moving to catalina.

No… my NAS is connected to my LAN via ethernet just like any other device

Dave, is that not the answer you need?
It would explain your issue.