Formatting iMac 1TB fusion drive?

[Leo]

By my or Mac (late 2012) error 1TB needs to br reformatted. It is not recognized anymore. It happened after my second attempt to restore Mojave from the Time Machine backup. The first restore was completed without problems. During the second attempt the TM backup was damaged and stop responding.

I have found on the Net a post, that advised to erase Mac Hard Drive in Disk Utility and follow. I think, that is a main problem why it is not being able to be restored from Carbon Copy Cloner.

Is the process too complicated.

I have good working Carbon Copy Cloner Mojave backup and able to run it on Mac but much slower.

Thank you.

 

[maccam]

By my or Mac (late 2012) error 1TB needs to br reformatted. It is not recognized anymore. It happened after my second attempt to restore Mojave from the Time Machine backup. The first restore was completed without problems. During the second attempt the TM backup was damaged and stop responding.

I have found on the Net a post, that advised to erase Mac Hard Drive in Disk Utility and follow. I think, that is a main problem why it is not being able to be restored from Carbon Copy Cloner.

Is the process too complicated.

I have good working Carbon Copy Cloner Mojave backup and able to run it on Mac but much slower.

Thank you.

Is your fusion drive still a fusion drive? If it is, it should report as being something like 1.12TB and not 1TB. If it is showing 1TB you will have to create a fusion drive in "Terminal". The instructions for that are on Other World Computing web site. I've had to do that twice.

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Good luck

JAW

 

[Leo]

Thank You!

The dive is still 1.12TB. I will read, try and report
Leo

 

[Leo]

Hi,

Back to yo with the question.

Reading step by step (by Apple support) "How to fix a split Fusion Drive". which is probably reformatting the Fusion drive.

My Fusion drive is not accessible. When I start Mac by holding COMMAND + R without plugged to USB a bootable backup external drive, the blank starting screen displays only rotating globe and asks to "Choose Network" from the list of WIFI networks.

When I start Mac with plugged to USB a bootable backup external drive by holding COMMAND + R, I will login to Mojave installed on the connected bootable backup drive.

My question:

Is my BOOTABLE BACKUP safe? Would the Terminal start working on my Backup Drive instead of the Fusion Drive? I afraid to loose it.

Procedure:

If you're using macOS Mojave

1. Turn on your Mac, then immediately press and hold Command-R to start up from macOS Recovery. Release the keys when you see the Apple logo or spinning globe.
2. When you see the macOS Utilities window, choose Utilities > Terminal from the menu bar.
3. Type diskutil resetFusion in the Terminal window, then press Return.
4. Type Yes (with a capital Y) when prompted, then press Return.
5. When Terminal indicates that the operation was successful, quit Terminal to return to the macOS Utilities window.
6. Choose Reinstall macOS, then follow the onscreen instructions to reinstall the Mac operating system. Your Mac restarts from your Fusion Drive when done.

Leo

 

[JPAlbert]

OP:

If you have a CCC cloned backup, try BOOTING FROM IT.
THAT'S WHAT IT'S FOR.

1. Power down, all the way off
2. Connect the CCC cloned backup
3. Press the power on button
4. Immediately hold down the option key and KEEP HOLDING IT DOWN
5. The startup manager will appear. Select the cloned backup and hit return.
6. The Mac will start from the backup drive. IF it's a platter-based drive, it may take longer to boot (depends on the drive, whether it's USB2 or USB3, etc.)

You should be able to log in and get to the finder.

Now you can "attack" the internal fusion drive and get it right.

Open Disk Utility.
Go to the "view" menu and choose "Show all devices".
Now you can see everything, including the physical drives.

At this point, you'll have to see what options Disk Utility offers for erasing and rebuilding a fusion drive. I've never had one, so I'm not sure how this is presented to the user in DU.

I'm not sure if you have to erase BOTH portions of the fusion drive (the SSD portion and the HDD portion) individually and "re-fuse" them, or not.
DU may offer to do this automatically. I'm not there to see, so I just don't know what it looks like.

You will want to get the drives inside erased and "refused", and be essentially "empty". For Mojave, erase them to APFS with GUID partition format.

Now you can open CCC (again while booted from the cloned backup), then RE-clone the backup BACK TO the fusion drive.

Not hard, just takes some time.

 

[Tom_N]

From this and other threads, It sounds like the OP tried to downgrade from Catalina to Mojave without formatting the Fusion Drive first.

FYI: Catalina splits an APFS-formatted startup drive into two APFS volumes: a read-only one, and a read-write one. I don't know what needs to be done about this.

 

[Leo]

WOW!

“Not hard. just takes time”

Hard not to agree after reading your post. Some steps are familiar and some are not.

I will go every step and try it. The HD backup CCC external in your descired procedure is SAFE!

I hope you know, if by the info shown below your steps would work. It seems that CATALINA has split Macintosh HD into four drives:

Disk Utility shows TWO!!!: “Macintosh HD” are empty (few megabytes, kilobytes)

Disk Utility shows TWO!!!: “Macintosh HD - Data” are also empty (few megabytes, kilobytes)

Shown below is the screen copy (numbers) of > Utility>Terminal: diskutil list.

My time is 9:47 PM. I will try tomorrow and will post results. I hope for a winner!


These are numbers bytes on the split Macintosh HD

 

[Leo]

Thank you for helping!

That what I have also a question about, as do not know the answer.

I have follow advice to erase drive, which has sounded reasonably, as there was a message to erase drive. Erase has not deleted extra drives but erase data. However the data was also spelled as the drives. Even erasing one of four should be disaster

There is a post from Apple, which I will try to understand, if it can be applied empty drives. I do not think that doing it would make the bad situation worse. The drives are empty anyway. (data in my reply to JPAlbert.

HOW to Fix a split Fusion Drive

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

 

[Tom_N]

I have follow advice to erase drive, which has sounded reasonably, as there was a message to erase drive. Erase has not deleted extra drives but erase data. However the data was also spelled as the drives. Even erasing one of four should be disaster

Formatting a Fusion Drive will erase everything on it – or at least, everything on the main part of the drive. (If you use Boot Camp on a Fusion Drive, it will create a HDD partition that is not part of the Fusion Drive proper.)

FYI,

The "Macintosh HD" / "Macintosh HD – Data" split is a result of Catalina trying to prevent you (and malware) from getting your hands on key system files. If I had to guess, I'd say that the reason you have two of each is that you have a Fusion Drive. Disk Utility might be breaking each volume down by its SSD and HDD sub-components.

The tiny volume sizes are probably because the Fusion Drive is formatted using APFS. A HFS+ volume has a fixed partition size, but an APFS volume can dynamically share free space with other APFS volumes in the same container. So these Macintosh HD volumes can be very small and still have access to the entire 1.1 TB in the Fusion Drive container.

 

[Leo]

I have completed step to fix a split Fusion Drive. The step in my response tomaccam (my second post). now instead of four HD Disk utility show one. Its name is MacintoshHD

Now I am in unknown territory.

Should I erase it? most likely Yes. If Yes, then what format I should use APFS or Extended Journaled?

Just have found the answer:

HOW to Erase Disk for Mac!!! (Apple support) - the link is below:

https://support.apple.com/en-us/HT208496

• macOS Mojave: The installer converts from Mac OS Extended to APFS.

Hilighted Macintosh HD selected Erase and done.

Now is the time to attempt cloning....

 

[Leo]

Thank you for all advices and the help!

My Mac is restored to Mojave from CCC copy. Now the process does not look like a complicated process, after all related questions were answered.

The Time Machine backup failed as after upgrading to Catalina Mac immediately started writing to it. I have stopped it as there was no message, no warning, It was good working backup as I have used it several times.

My CCC was not effected by the upgrade and it is simpler to use.

Here are my steps:

1) HOW to Fix a split Fusion Drive (Apple support)

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

2) HOW to Erase Disk for Mac!!! (Apple support)

https://support.apple.com/en-us/HT208496

3) Clone CCC backup to Mac HD

SUCCESS!

 

[Tobamory]

One thing about fusion drive was the earlier versions of Mac OS caused a real pain for us users when formatting it, I spent many an hour following threads on how to do it properly, the last 2 release of OS simplified this and it’s now as easy as a normal SSD

I have to say though the fusion drive when it starts to get full was one of the main reasons I decided to upgrade, dog slow when compared to an ssd, you could look at an external ssd for booting it seems to be the way most go when locked into a specific drive technology.
I had a blow out when I,upgraded got a 1tb SSD which with all my stuff on is only half full, think 1tb is sweet sport 512 is a bit too small for me anyway, my MacBook has 100gb left when I’ve got most of my stuff on.

i then bought a QNAP 472XT fully loaded it with memory nVME and big spinners and the benefit of this QNAP is it’s also thunderbolt 3 so it’s like having endless fast storage

but glad you fixed it , I bet you had one of those sweaty moments when you think your doomed, like I used to when trying to format the thing LOL

 

[Leo]

Thank you for the details!

My Mac SSD par of the Fusion Drive is small (250GB ?). As you said, it can be a reason for a slow start.

The Mac HD is shown as one piece. How can I verify its content and the content size?

The TERMINAl command: diskutil list shows four dives. Three for HD and one 2TB External.

 

[Tobamory]

Thank you for the details!

My Mac SSD par of the Fusion Drive is small (250GB ?). As you said, it can be a reason for a slow start.

The Mac HD is shown as one piece. How can I verify its content and the content size?

The TERMINAl command: diskutil list shows four dives. Three for HD and one 2TB External.

Its a good point I don't think you can, im pretty sure the Fusions were only 128gb.. I could be wrong though

My boot time were not that bad, but once into Mac OS it was dog slow at getting to speed..

 

[Tom_N]

Thank you for the details!

My Mac SSD par of the Fusion Drive is small (250GB ?). As you said, it can be a reason for a slow start.

Its a good point I don't think you can, im pretty sure the Fusions were only 128gb.. I could be wrong though

The SSD component is 128 GB in the first 1 TB Fusion Drives, and in all 2 and 3 TB ones. In recent 1 TB Fusion Drives, the SSD is only 24 – 32 GB.

 

[Leo]

I thought that my Fusion drive is 256MB, however do not remember.

Clicking on apple (upper left corner > About this Mac > Srorage

swos the bar named "Macintosh- HD" with color parts : green - Documents and Red - Apps.

That is all it shows.

 

[Leo]

Then it should be enough space for 8GB or so for macOS, if it has priority to be there ,

It is very slow starting now.

 

[Tom_N]

Then it should be enough space for 8GB or so for macOS, if it has priority to be there ,

You're being optimistic. Back in October 2015, 9to5Mac wrote that a 24 GB SSD would be small enough that "Waking the Mac from sleep would take longer" because the snapshot of your computer's memory could be too big to fit entirely into the SSD.

https://9to5mac.com/2015/10/13/retina-imac-fusion-drive-flash-lol-are-you-serious/

Anandtech reported that Apple uses 4 GB of the SSD as a write buffer. Suppose that you saved a Photoshop image. It would temporarily go to that part of the SSD (assuming that there was space) while the system decided on a long-term location.

https://www.anandtech.com/show/6406/understanding-apples-fusion-drive

 

[Tom_N]

It is very slow starting now.

That could be a couple of things. Perhaps a lot of the macOS files are on the hard drive and haven't been upgraded to a SSD location yet. The other thing that comes to mind is that if Spotlight decides to re-index your drive, that can really drag speed down until the re-indexing is finished.

 

[QBF]

Just wanted to say thanks for this.

I upgraded to Catalina at the weekend and strange things started to happen (poor safari performance, noisy fans, hard drive whirring all the time, hard drive space depleting overnight), so wanted to get back to Mojave. After waiting four hours for a time machine restore to complete, I was surprised to find Macintosh HD and Macintosh HD - Data.

Booted with internet recovery, was able to follow your instructions in Terminal and successfully initialise the fusion drive. Just got to wait another four hours to make sure it worked and everything is back to non-weird Mojave.