Problem factory resetting a new iMac 5K retina with 3 TB fusion drive

[SkotiPati]

Hello everybody,

I tried the usual factory reset procedure with my new Mac but have a serious problem with it.

I used cmd + R, entered disk utility, and tried erasing Macintosh HD but had the "Unable to delete the core storage logical volume" error so I can not reinstall the OS.

In disk utility I see 2 Macintosh HD one inside the other. They have unusual formats like logical volume group.

How can I factory reset a new iMac with fusion drive?

 

[ssls6]

Hello everybody,

I tried the usual factory reset procedure with my new Mac but have a serious problem with it.

I used cmd + R, entered disk utility, and tried erasing Macintosh HD but had the "Unable to delete the core storage logical volume" error so I can not reinstall the OS.

In disk utility I see 2 Macintosh HD one inside the other. They have unusual formats like logical volume group.

How can I factory reset a new iMac with fusion drive?

You can only delete the core storage volume (to my knowledge) from the command line. Inside the command shell you basically break the fusion into 2 and then refuse it.

Did you select the "2nd" Macintosh HD entry and hit "erase"? The one that indented?

 

[SkotiPati]

You can only delete the core storage volume (to my knowledge) from the command line. Inside the command shell you basically break the fusion into 2 and then refuse it.

Did you select the "2nd" Macintosh HD entry and hit "erase"? The one that indented?

Thanks you ssls6,

Yes I tried the second Macintosh HD and got the error.


From my further scan through many forums I think I need to do this:

(please verify these procedures if you can)


1) Open the computer with "cmd + R"

2) Open Terminal

3) diskutil cs delete <Paste UUID of Logical Volume>

4) diskutil cs delete <Paste UUID of Logical Volume Group>

5) Go into Disk Utility

6) Let the Disk Utility fix the Fusion drive from scratch

7) Reinstall the OS to the new Fusion Drive


Some web sites only tell me to delete Logical Volume Group but others say that you need to first delete the Logical Volume and then the Logical Volume Group.

It's all French to me

If someone verifies this action list, I'll do it.


Thanks.

 

[Weaselboy]

Don't worry about the UUID. Just do this to nuke the CS volume. Type it exactly like this including the quotes.

diskutil cs delete "Macintosh HD"

 

[SkotiPati]

Don't worry about the UUID. Just do this to nuke the CS volume. Type it exactly like this including the quotes.

diskutil cs delete "Macintosh HD"

Are you sure?

Because there are 2 Macintosh HD originally created by Apple. One has Format of Logical Volume Group, the other Logical Partition.

With the code you recommend which one will be erased?

From what I understand you have to delete them in order to completely format both the HD and the SSD of the Fusion drive in iMac. And then let Disk Utility to create a Fusion Drive from 2 empty drives by Fixing.


thanks weaselboy

 

[Weaselboy]

Are you sure?

Yes... trust me, I'm from the Internet.

That is just one hard drive as you know, and it looks that way because of the virtual (logical) drive created by the core storage conversion for Fusion.

When you run that command they will both be gone and you will be left with the drive itself showing and no formatted partitions.

 

[SkotiPati]

Thank you Internet!

I'll try and let you know about it.

Best.

 

[SkotiPati]

Weaselboy you are my sunshine!
Thanks a lot.

I think I did it. The only difference from the original Apple structure is there are no longer 2 macintosh HD drives one being the volume geoup the other being the partition.

Now group is called Internai Drive. Partition is Macintosh HD.

Also originally disk0 was SSD and disk1 was HD. Now its the reverse.

I attached the final structure. Is everything ok? I think it is.

 

[Weaselboy]

Yep... looks like you are in good shape there!

 

[designbot]

Thanks! You saved my bacon.

 

[auslad88]

thanks for this ! This worked for me too - so very grateful!