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The_Family Author

Level 1

8 points

Why is PB/EB visible in the partition menu of disk utility

I have a fusion Drive on iMac (Retina 4K, 21.5-inch, Late 2015) . I only received the machine yesterday from Ebay. It has Catalina 10.15.7 on (basket of eggs user logon which I coded) . It says 1 TB but I think the disk is 2TB at least. I tried partitioning it and did some root. I think the following is of relevance in regard to the data disc that did my head in when I was recoding Catalina for Apple on the lowdown. Any comments ?

Depending on the OS which is booted it may be possible to narrow the list down even more using the "physical" option, but this is only available in recent versions of macOS (may just 10.13+ ?).

diskutil  list  internal  physical

Then you use the following command to write zeroes to the beginning of the drive making sure to replace the "diskX" portion of the command with the correct drive identifier for the physical drive needing erased after first making sure to unmount all volumes on the physical drive:

diskutil  unmountDisk  diskX

sudo  dd  if=/dev/zero  of=/dev/diskX  bs=100m  count=10

iMac 21.5″, macOS 10.15

Posted on Oct 7, 2021 5:11 AM

Top-ranking reply

HWTech

Level 9

59,840 points

Posted on Oct 7, 2021 7:07 PM

I'm not entirely clear on your issue other than you have an iMac you purchased from eBay and it has a Fusion Drive. You are not sure if you have full access to all the storage on the Mac. Other than that I don't understand your post.

When purchasing a used computer you should always perform a clean install of the OS by first erasing the entire physical drive (or in this case the entire "Fusion Drive") before installing macOS. This will give you a nice clean version of macOS. Doing this will also alert you to whether the used Mac has a firmware lock enabled or whether the Mac is still being managed by a previous owner plus you don't have to worry about any nasty surprises left behind by the previous owner.

If you can log into the Mac, then I highly recommend creating a bootable macOS USB installer using the instructions in this Apple article so that you have more options if something goes wrong:

https://support.apple.com/en-us/HT201065

Or you can boot into Internet Recovery Mode using Command + Option + R to access the most recent version of the online macOS installer that your iMac supports which at this time is macOS 11.6 Big Sur.

After booting the macOS installer launch Disk Utility and select the "Fusion Drive" on the left pane and erase it as GUID partition and APFS (top option). Quit Disk Utility and select "Reinstall macOS".

FYI, here is what the previous owner should have done prior to selling the Mac (even if they did a clean install, I personally would do it myself to be sure the system is clean and to know there is no firmware lock and that it is not being managed):

https://support.apple.com/en-us/HT201065

The commands you quoted here were commands I suggested another user perform who was unable to erase their drive after installing a non-Apple OS and really don't have any bearing for your situation. If you wanted to completely refresh the Fusion Drive, then you could intentionally break the Fusion Drive setup and recreate it although I don't think this is necessary here although I would personally do so if it was my computer because why go to all the other work without refreshing the base which is the Fusion Drive.

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Why is PB/EB visible in the partition menu of disk utility

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