Hard drive question on "new" iMac

OK, your iMac was originally available in 4 different storage options:

• 1 TB HDD
• 1TB Fusion drive w/24GB SSD
• 256 GB SSD
• 512 GB SSD

I think it most likely has an original 256GB SSD. (If it were somehow a split 1TB Fusion drive you would only be seeing a 24GB SSD.)

For reference, here is a complete rundown on your model --> Apple iMac 21.5-Inch "Core i5" 3.0 (4K, Mid-2017) Specs

I believe there's nothing to worry about here unless you're concerned about having paid for a 1TB HDD but "only" got a 256GB SSD ... although having 16GB RAM instead of 8GB is a real blessing.

The unit appears to have / had a Fusion Drive that no longer is seen as one.

That would explain the smaller SSD; another unknown larger storage is the

other portion, usually a rotational hard drive accessed through the SSD drive.

So something happened to the Fusion drive to make it appear broken.

I've never had a Mac with one of those, it's a hybrid idea where the

heavy lifting is done by the SSD & the HDD helps supply bulk storage.

What needs to be done, is try and figure how to re-enable the Fusion

connection between the smaller SSD and larger Storage hard drive.

The specs seemed a bit high for such an uncharacteristically small drive.

Just looked up the Apple Support article. This may apply..

..I did not think that I had it bookmarked; but did.

If your model checks out as one with Split Fusion drive:

• How to fix a split Fusion Drive - Apple Support

https://support.apple.com/en-us/HT207584

"IF your Fusion Drive appears as two drives instead of one in the Finder,

it's no longer working as a Fusion Drive. Here's how to fix it."

[The instructions tell how to test and see what your Mac has

and now to fix the problem to restore the missing portion.]

To find out what may be missing, since the serial number didn't work to

look up the iMac, was all the other specs you wrote. Everymac was one

of two sites with an ultimate lookup; & your model shows with a Fusion.

Some of those with a 1-TB (5400/7200-RPM) hard drive, do not use a SSD.

So that appears to be the reason for two hard drive icons; but, one is not

at all there. (Evidence suggests a Fusion drive; partially disconnected.)

..Edited: to include other found information on Fusion drive..

..MartinR:

The remaining screenshot, that hosts 'did not remove' due to Serial number,

still shows two drive names. But uncharacteristically, both same capacity.

[And missing with actual drive report, are progressive partition numbers.]

And both the same size. The iMac shipped with larger drives;

A Fusion, once broken, would not find its rotational portion.

He could get and run DriveDx, to see exactly what the item is; or is not.

https://binaryfruit.com/drivedx

And an ASC instructional User tip: "How to use DriveDx"

https://discussions.apple.com/docs/DOC-250004005

That utility has 'several free-trial runs' before it shuts down.

The link I'd posted previously, could help determine HDD/Fusion status.

That version of higher CPU iMac normally has larger storage stock drives.

But whatever the thread author decides; I just provided the means

for him to check the unit. [With or w/o Command-line instructions.]

..Anyway, didn't help the entire image was removed due to a Serial Number.

I'd checked that; and there was nothing in three SN report databases, on it..

Did you also check the earlier thread where this matter was discussed?

[Any Time Machine may still be relevant if that contained a Fusion from SSD.]

PS: A notification from Martin arrived, but not from Steve!

I see both in ASC but not from email I usually get.

The Disk Utility screenshot looks normal to me. So does the System Information screenshot.

I'm not convinced it's a split Fusion drive. It appears to be just a 250GB SSD. (I don't believe Apple's fusion drives ever had more than a 128GB SSD flash storage section.)

Steve Scherf1 - Open Disk Utility again. Then in the menu strip, select View > Show All Devices. The left pane in Disk Utility should then look something like this:

You can also select the top level device in Disk Utility (in my example APPLE HDD ST1000DM003 Media) and Disk Utility will show you what the entire storage device capacity is.

Please post a screenshot for comparison.

Normally the APFS container has two Volumes that are illustrated as "disks:" Macintosh HD and Macintosh HD - Data. You may have renamed them (knowingly or not).

Looks normal to me.

It will help if you can tell us exactly what model iMac this is. Go into System Information > Hardware. It should look something like this:

Also, under About This Mac, it will say something like "iMac (Retina 5K, 27 inch, late 2017)."

When your system drive is formatted as APFS, macOS creates an APFS Container and by default the Container is the entire disk regardless of whether it's an SSD or an HDD. And when you install macOS, the installer creates 5 Volumes inside the Container, only 2 of which are normally visible: Macintosh HD and Macintosh HD - Data. The other 3 are hidden and are used for for recovery and system use.

Macintosh HD is a Volume that contains the macOS system. It's read only and can only be modified by Apple (through installation of macOS or a macOS update such as a Security Update).

Macintosh HD - Data is also a Volume and it's the one you can write to. It contains user-installed applications as well as all user data.

macOS does some magic behind the scenes to link Macintosh HD and Macintosh HD - Data so they appear to be a single "disk" called Macintosh HD in the Finder.

A previous owner/tech may have installed an SSD but the stock ones for that model are nearer 1-TB on the upside.

Anyway, the Drive Dx is a superior utility; also EteCheck does much. and could report some issues.

I'm done.

Good luck!❄️🍄🌼

It would also be a good idea to contact the seller and get them to verify how they configured your "new" iMac.