iMac Partitioned Spontaneously (It Seems)

Question

iMac Partitioned Spontaneously (It Seems)

Hi,

Thank you in advance for any help or comments you can provide.

Here are my computer specs:

iMac: 21.5-inch, Late 2013

Processor: 2.7 GHz Quad-Core Intel Core i5

Memory: 16 GB 1600 MHz DDR3. (“Your Mac contains 2 memory slots, each of which accepts a

1600 MHz DDR3 memory module.”)

Storage: 1.12-TB fusion drive

I am the only person who uses this iMac. I am the only “User” on the hard drive. Nobody ever borrows this iMac. I have never needed nor wanted to partition my iMac. I have never attempted to partition my iMac. (I don’t know how to partition an iMac.)

This was my problem (that I’m hoping to avoid in the future):

Computer would not boot up. Started computer in recovery mode, ran Disk Utility. First aid on hard drive went reasonably quickly. However, first aid on my 2TB external hard drive (for Time Machine backups) lasted maybe five (5) hours.

Computer still would not boot up.

Started computer in recovery mode, reinstalled OS (Catalina).

Computer still would not boot up.

Started computer in recovery mode, erased HD and reinstalled OS (Catalina). During data migration, computer indicated that I didn’t have enough space for the migration. I.e., computer said I only had approximately 200 GB of space. (Supposed to have 1 TB.)

Did this step again (erased HD & reinstalled OS) to see if my computer would recognize 1 TB of space. Again, computer said that I only had approximately 200 GB of space.

Took my computer to a local brick and mortar repair shop. She did get my computer to what appears a normal state. Here are her notes on her invoice:

Fused hard drive – hybrid drive in multiple partitions. Reinstalled Yosemite. Updated to Catalina. Restored files and updated Apple ID.

Questions for the Apple Community:

How can I avoid this happening in the future? (Unwanted / unneeded partitions.)

How did my computer get partitioned?

How did I end up with only approximately 200 GBs of memory (according to my iMac in recovery mode).

Thank you so much! I appreciate your help.

iMac 21.5″, macOS 10.15

Posted on Mar 31, 2022 12:44 PM

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Answer 1

Best reply

HWTech

Level 9

56,126 points

Apr 1, 2022 9:27 AM in response to anonymous-imac-user

macOS now has two APFS volumes tied together to form the traditional "Macintosh HD" item which people are used to seeing, however, in reality this "volume" is now two separate volumes magically linked together behind the scenes. There is now a read-only macOS system volumes (macOS itself titled confusingly enough "Macintosh HD" by default) and a read+write volume for user data (user accounts & volatile macOS data/files -- titled "Macintosh HD - Data" by default, or even just "Data" depending where you look). See these Apple articles for some details:

About the read-only system volume in macOS Catalina - Apple Support

https://support.apple.com/guide/security/signed-system-volume-security-secd698747c9/web

If you don't erase the whole drive (Intel only) or Container, then you can get two copies of your data stored on the drive. You can see the instructions in this Apple article for reinstalling macOS properly:

How to reinstall macOS - Apple Support

You must click on links within that article in order to get the instructions for a clean install by first erasing the drive (don't assume you know the proper way to erase a drive these days since the drive layout has been changing drastically over the last few years and can have slight variations between Intel & M1 Macs). Here are links from the other article for actually erasing a drive for a clean install:

Use Disk Utility to erase an Intel-based Mac - Apple Support

Use Disk Utility to erase a Mac with Apple silicon - Apple Support

With 2018+ Intel Macs with the T2 security chip and the newer M1 Macs, it is also possible to "Restore" the firmware to also reset the security enclave of the T2 & M1 Macs as well as the traditional clean install.

https://support.apple.com/en-eg/guide/apple-configurator-2/apdebea5be51/mac

https://support.apple.com/guide/apple-configurator-mac/revive-or-restore-a-mac-with-apple-silicon-apdd5f3c75ad/mac

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Answer 2

Mar 31, 2022 3:14 PM in response to ku4hx

Hi ku4hx,

Thank you for your input. I appreciate it.

When you say that you've seen it before, do you mean that you've seen partitions created when reinstalling the OS?

Also, it happened twice (showing only ~ 200 GB of space after erasing the HD and reinstalling the OS).

Also, embarrassed to admit this, but a few hours before my computer problems cropped up, I had clicked a link in an email that I thought was from Amazon (it wasn't). I'm wondering if this had anything to do with my computer issues.

Thanks again!

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Answer 3

Mar 31, 2022 3:15 PM in response to ku4hx

Hi ku4hx,

Thank you for your input. I appreciate it.

When you say that you've seen it before, do you mean that you've seen partitions created when reinstalling the OS?

Also, it happened twice (showing only ~ 200 GB of space after erasing the HD and reinstalling the OS).

Also, embarrassed to admit this, but a few hours before my computer problems cropped up, I had clicked a link in an email that I thought was from Amazon (it wasn't). I'm wondering if this had anything to do with my computer issues.

Thanks again!

Reply

Answer 4

ku4hx

Level 7

23,472 points

Apr 1, 2022 10:04 AM in response to anonymous-imac-user

I've seen all sorts of anomalies when the process was not performed correctly. One thing you need to be aware of, the process properly creates two Macintosh "drives": Macintosh HD which is your system, and Macintosh HD - Data which is your user data.

There's no telling what a malware link can do. It you installed malware you can expect something well ... unexpected.

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Answer 5

Apr 1, 2022 11:49 AM in response to HWTech

HWTech,

Thanks so much for your input. That's a lot of information and I'll have to reread it.

I did notice, in my Time Machine backups, that there were the "Macintosh HD" and "Macintosh HD - Data" folders.

Who knew erasing a drive wasn't so simple. Apple Care was on the phone with me both times that I tried to erase the drives, so I guess it's really not that simple.

Thank you again.

Reply

Answer 6

Apr 1, 2022 11:57 AM in response to ku4hx

ku4hx,

Thank you for answering my follow-up question.

I had noticed, in my Time Machine backups, two folders with the names "Macintosh HD" and "Macintosh HD - Data."

I was on the phone with Apple Care all 3 times that I tried to reinstall the OS. I guess it's not that simple to do.

Malware ... what a pain.

Thank you again!

Reply

Answer 7

ku4hx

Level 7

23,472 points

Mar 31, 2022 2:54 PM in response to anonymous-imac-user

My guess is you made an error in reinstalling the OS. I've seen it before.

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iMac Partitioned Spontaneously (It Seems)

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