Use internal drive as a backup?

[golfgirlgolf]

I have a 2019 27" iMac 3.7GHz 6 Core 64GB with internal 2TB Fusion drive. For a long time now I've been Booting from an external SSD (Samsung 980Pro in an ACASIS enclosure - very fast) - currently Big Sur but going to start upgrading MacOS. Meanwhile the internal Fusion drive has been running, but completely unused.

Before I upgrade, I was hoping to clone the boot SSD - to the internal Fusion drive - and then set it up maintain it as a regular daily backup of the SSD. Turns out, that's not so simple.

I first tried the bootable backup in Chronosync using the bootable backup feature - it crashed.
I tried Disk Utility/Restore to create the same backup scheme - boot SSD>internal Fusion - that didn't work out
Super Duper then had the error - "the source volume cannot be restored because it has a broken seal" - which apparently is a Big Sur issue that requires some work to get around.

Q1 - Will updating my Big Sur boot SSD to Monterey make it able to clone to the internal Fusion HDD?
Q2 - I also have Time Machine running on the boot SSD - can I restore it to the internal Fusion - or am I going to have the same (Big Sur) problems?

Any other way to get this done? I really don't want to crack the case and replace the Fusion HDD with an SSD. It's just too risky/gooey.

 

[ignatius345]

It sounds like something is wrong with the Fusion Drive. I'd say just "de-fuse" it so the OS sees it as two separately formatted drives. You're getting no value from it being a Fusion Drive, and it's just another point of potential failure to leave it like that. De-fusing it will leave you with a big HDD for backups and a fast little internal blade SSD (128GB maybe?) that you can use for whatever.

 

[golfgirlgolf]

It sounds like something is wrong with the Fusion Drive. I'd say just "de-fuse" it so the OS sees it as two separately formatted drives. You're getting no value from it being a Fusion Drive, and it's just another point of potential failure to leave it like that. De-fusing it will leave you with a big HDD for backups and a fast little internal blade SSD (128GB maybe?) that you can use for whatever.

Thanks for the reply. No I don't think there were any issues with the internal Fusion drive. The errors I seemed to be getting were due to the source volume (being Big Sur) apparently.

I tried a couple of things but the one that seems to have worked -
Recovery Mode - format/reinstall Big Sur on the internal Fusion drive.
Ran a full restore from the most recent Time Machine backup (of the boot external SSD drive)

The result seems to be mostly a clean copy of the boot external SSD drive - on the internal Fusion drive.

One caveat - I'm getting two volumes for (the internal) Macintosh HD now - one extra one that is Macintosh HD - Data
Only one appears on the desktop, but two show in the Finder/Locations menu - other drives that have the same configuration do not show 2x in that menu. This might be something that's a Time Machine artifact. See attached screenshot - Fusion Drive (restored from a TM copy of the external Samsung 980 SSD.) versus how the SSD looks on it's own.

Once I get this sorted, I'm hoping a daily incremental backup of the boot external SSD - to the internal Fusion drive - will work well. At least until I upgrade my Mac to one with a large SSD inside.

 

[Fishrrman]

Looking at the rightmost pic above in your OP:
Have you tried clicking the TOPMOST item in "the list on the left" ("Fusion Drive") and then erasing it ?

That is, don't erase the "container" we see below it.

Seems to me this will erase the entire fusion drive, and not "the container"...

 

[golfgirlgolf]

Looking at the rightmost pic above in your OP:
Have you tried clicking the TOPMOST item in "the list on the left" ("Fusion Drive") and then erasing it ?

That is, don't erase the "container" we see below it.

Seems to me this will erase the entire fusion drive, and not "the container"...

Hmmm - OK I see what you're saying. Recovery mode might not have automatically formatted on the root level when I reinstalled Big Sur. :-/ Looks like I will have to try the process again - making sure to go into Disk Utility and manually format(erase) the Fusion drive at root level before going to the next step.