Unable to access user data on split iMac hard drive

This old iMac may have been configured with both a HDD and an SSD as storage devices. That was an option in that mid-2011 model. Though it was not a "Fusion Drive" configuration.

If you're sure the iMac had only the single HDD, it may simply have been partitioned into two or more volumes and then the data should still be on it, unless there is some problem with the drive. An OEM drive for that Mac will now be about fifteen years old and may very well be operating in a state of failure. Accessing additional data may require disk management diagnostics and tools.

You do actually use the word "split" and that is typically a reference to the Fusion Drive that some Macs were configured with from the factory. AFAIK, the mid-2011 iMac was not available with that option.

Are you certain of the year of that iMac?

The late-2012 iMac could be had with a Fusion Drive. A Fusion Drive, when split, would present performance problems for the iMac. If you pull only the HDD from a Mac with a Fusion Drive, you leave behind the SSD component with 256, 512 or 768 GB of storage potential.

The OP has another thread over here where they provided some extra details such as receiving a "-36 error" which translates into an "I/O Error":

https://discussions.apple.com/thread/256390434

Since the OP seems to have ignored their other thread......I will repost my response from that post:

Error code -36 indicates an I/O Error. This could indicate a hardware issue either with the SSD itself, or the USB connection to the Mac, or it could indicate some file system corruption.

Personally I would start with making sure the SSD is healthy. Run the third party app DriveDx (free trial period) and post the complete text report here so I can examine the report for clues (Ignore the summary results). You will need to install a special USB driver in order to get access to the external USB SSD's health information. Do you have access to another Mac from 2007 to mid-2014? Once we have this information, then we can determine the best course of action.

Plus in that other thread macOS 10.9.5 is referenced along with wishing to recover the various macOS libraries such as iTunes, iPhoto, etc. which does change things a bit here as well if that is true.

Plus if the drive involved here is actually a Hard Drive (hard to tell from the way the posts are written), then I suspect a failing drive which means the OP should be very careful to minimize the use of the drive they wish to have data recovered since the more the drive is used, the worse the failure will become where even a professional data recovery service may be unable to recover any data. Most data recovery software doesn't know how to deal with the I/O Errors produced by a failing drive as they are made for recovering data from a healthy drive. macOS also is unable to deal with I/O Errors which is why I have never used a macOS host for recovering data from a failing drive.

ATLN wrote:

It does not appear to be a Fusion Drive. I am certain of the year.

Even if I might miss something stored on an SSD component that I did not see in there before the rest of the iMac was ditched (and wouldn't this only be sort of "recent stuff"?), would not the primary operating system and main user info be on the core hard drive? None of this is visible on this current hard drive, which makes me think there is some incompatibility with my current macbook pro and reading or recognizing the contents of the externally connected hard drive.

If a 2011 iMac then certainly not a Fusion Drive.

As to what might be stored on an SSD in an iMac of that vintage, it could be anything that the user wished to store there and not limited to "recent stuff".

As for the OS and main user, if I had an iMac with both an HDD and SSD installed inside, I would likely install the OS on the SSD if for no other reason than the SSD would provide the better performance and operational speed than the HDD. If the OS is installed there, one would also expect the user folder(s) to reside on the SSD as well. I would use the HDD for file storage unrelated to the OS.

If that drive is working properly there will be no incompatibility of the drive hardware with your MacBook Pro. Your MBP should be able to recognize the drive format and access any folder and files stored on it.

Can you give us a snapshot of what Disk Utility sees when you connect that drive to your MacBook? Its info would be listed in the sidebar under the heading "External". In DU you might want to click View > Show All Devices after you launch it.

Have you attempted to run Disk Utility's First Aid routine on the drive? Perhaps there is some directory corruption that needs to be identified and repaired.

Your MBP should have no problem reading and writing to that external drive if it is working properly and not corrupted.

Apple_HFS is the normal identifier for a pre-Mojave (10.14) Mac startup drive formatted as Mac OS Extended (Journaled).

MacOS since Mojave (Catalina?) has required the disk drive format to be APFS to be used as a startup disk, which is why your newer MBP reports that.

Can you please show us a screenshot of the Terminal window displayed when you use the diskutil list command?

A screenshot of the Disk Utility window might also be helpful.

Were you able to successfully run the Disk Utility First Aid on the drive?

I suspect either the drive directory structure is corrupt or this drive does not have on it the data that you think it should.

I checked the specs for the mid-2011 A1312 iMac models and they all appear to have come with a standard HDD or SSD, not a Fusion drive, so I don't understand how it could have been "split." That's a Fusion concept. Do you mean "partitioned?"

Be that as it may, what is the format of the drive (I assume it's MacOS Extended Journaled but want to verify). If partitioned, do you see both partitions? What version of OS X/macOS was on it? What are the folders you do see? Do they have contents?

Not to alarm you, but the Hitachi Deskstar drives did not have a great rep.

Based on your drawing,

If this was the only drive in the Mac and it had 2 partitions, the one you are seeing would appear to be the 2nd partition and it was probably data only (meaning no OS installed on it).

• • There would have been an OS installed in the second partition only if your parents had set up the Mac for "dual boot" in whch case a version of macOS would have been installed on both partitions. But it doesn't look like that to me.
  • If it was partitioned with 2 partitions and you are only seeing 1 of those partitions then there is something wrong with the drive.
  • In the lower drawing is the "Macintosh HD2" the same drive as the "Macintosh HD ⇪" in the upper drawing?

If this was the 2nd of 2 drives this was probably a data drive, meaning that it had no operating system installed on it.

Does Disk Utility show two partitions on this drive?

It's also possible that the drive just went bad over time.

You could try using Prosoft Data Rescue to scan the drive to see if there are any recoverable folders/files. You can recover up to 1 GB of files for no charge; after that you have to buy a license. I have used it myself and it works very well.

Must be partitioned. When I had connected my macbook pro to the iMac itself 2 years ago, I had seen 2 HDs, with non-duplicated data. Now with just the extracted hard drive connected to my macbook pro, I do NOT see both partitions. From what I can figure, I appear to be viewing simply the folders from the Desktop of one of the two partitions. The format is MacOS Extended Journaled. I am unsure of the OS X/Mac OS version and am not able to see any System or User or Library paths on this hard drive at this time (that is part of the issue).

It does not appear to be a Fusion Drive. I am certain of the year.

Even if I might miss something stored on an SSD component that I did not see in there before the rest of the iMac was ditched (and wouldn't this only be sort of "recent stuff"?), would not the primary operating system and main user info be on the core hard drive? None of this is visible on this current hard drive, which makes me think there is some incompatibility with my current macbook pro and reading or recognizing the contents of the externally connected hard drive.

*Correction - as clarified in responses, this is likely a partitioned hard drive, NOT a split hard drive.

Secondly, here is a drawing that might help clarify my issue.

[Edited by Moderator]

Disk Utility GUI sees "Macintosh HD2" only when "Show All Devices" is checked. If it helps, on Terminal, diskutil list shows the type as Apple_HFS (while my macbookpro is Apple_APFS).