2012 27 inch iMac - 2x 3.5 drives?

[InuNacho]

Hey folks, I picked up a 2012 27 inch iMac from a second hand store and and was surprised that it is the i7 GTX 680 CTO model.
I was installing High Sierra on it to test it out and noticed that there are 2x 3.5 HDDs inside of it, or am I confusing things?

If it is indeed 2x rotational HDDs, how can I set it up for a bootable RAID 1 for Mojave?

 

[nambuccaheadsau]

Well the options are a 3TB 7200rpm rotational drive, or maybe a 3TB Fusion Drive with the 3TB rotational anda 128GB PCI-e blade which maybe has died .

Go into Fisk Utility and see if that helps. The pics you have shown are normal for a 3TB rotational only.

 

[InuNacho]

Here it is in Disk Utility. I see 2 rotational drives with the OS installed on one and the other being empty.

 

[PaulD-UK]

Its one HD, formatted APFS, with the usual two containers - one read-only for System, one for Data.

 

[InuNacho]

Its one HD, formatted AFPS, with the usual two containers - one read-only for System, one for Data.

What are containers? On my Mac Pro I have 7 drives in it but each is an individual drive. I looked up the model number on the HDD and it says its a 3TB drive? On this iMac theres 1x 3TB drive that split into 2x 3TB things?

 

[PaulD-UK]

It seems like your iMac has had MacOS 10.15 Catalina on it in its previous life:

"macOS 10.14 or later uses a file system called Apple File System (APFS), which allows space to be shared between volumes on a disk. If a single APFS partition (or container) has multiple volumes, the container’s free space is shared and can be allocated to any of the volumes as needed. Each volume uses only part of the overall container, so the available space (shown in white in the illustration above) is the total size of the container, minus the size of all volumes in the container. This overall amount of used space, including other volumes in the container, is indicated by a cross-hatched area."

See if your Mac shares space across APFS volumes in System Information

In macOS 10.14 or later, the APFS file system features space sharing.

support.apple.com

High Sierra was the first macOS to use the APFS disk file system, so if you didn't erase the disk back to HFS+ it still had its APFS container system from MacOS 10.15 - with System and Data volumes.
So, it has one container, two volumes, which share the same physical disk space.
Which is what your screenshots show.

If you change DiskUtility's menu settings to show View>Show All Devices
then you should see the full disk format scheme.