Corrupted macOS hard drive

[Haole Boy]

Customer has 2 iMacs, a dead one and a working one. The task at hand is to transfer the system from the dead iMac to the working iMac. My plan was to boot the good iMac using the drive from the dead iMac mounted in a USB attach docking station. Unfortunately, the HD shows up as "unformatted" when looking at it in the good iMac.

Made a back up of the HD using ddrescue on my Linux machine. Finished with 100% copied (i.e. no bad sectors - so this is not a hardware issue).

Booted the good iMac and ran Disk Utility and tried First Aid on the bad HD. It failed. Looking at the disk util log file, I see the following lines:

Performing fsck_cs -n -x --lv --uuid 4945FCF1-C98F-4F25-BD6B-5A46C24FFDBA
Checking volume
disk2s2: Scan for Volume Headers
disk2s2: Scan for Disk Labels
Logical Volume Group 4945FCF1-C98F-4F25-BD6B-5A46C24FFDBA spans 2 devices
Incomplete or inconsistent CoreStorage Physical Volume set
Storage system check exit code is 1.

I'm no expert on macOS file systems, but this seems to imply there should be a 2nd drive somewhere. Can this be an external USB drive? Other explanations? (full disk util log attached to this post).


Mahalo,

Harry Z

 

[Markverhyden]

Hmm..... Two words come to mind after looking at the log. Fusion Drive. The SSD will be in a slot on the motherboard. Go to https://everymac.com/ultimate-mac-lookup/, plug in the serial number and you should be able to get the as built BoM.

 

[lcoughey]

Yes....whatever you do, keep the SSD and hard drive together. 100% of fusion drive cases sent into my lab after a technician were impossible to recover the file system because the tech overwrote the SSD.

 

[sapphirescales]

Screw this. Make a manual backup of the data and do a fresh install on a new HDD or SSD. Fusion drives are a PITA.

 

[Haole Boy]

Screw this. Make a manual backup of the data and do a fresh install on a new HDD or SSD. Fusion drives are a PITA.

OK. How do I do this when the machine this drive came from is dead? I have no way to access the file system on this drive.

Hmm..... Two words come to mind after looking at the log. Fusion Drive. The SSD will be in a slot on the motherboard. Go to https://everymac.com/ultimate-mac-lookup/, plug in the serial number and you should be able to get the as built BoM.

How did you conclude that this machine possibly has a Fusion drive?

everymac.com does not specify if this particular iMac has the Fusion drive. Just says it is optional. So, I guess I'll have to open it up again and see what's there. If I do find the 128GB SSD, how do I use it to complete the logical volume group and get data from the HDD? Do I have to purchase an external enclosure to put it in?

Mahalo for your responses

 

[overburnz]

OK. How do I do this when the machine this drive came from is dead? I have no way to access the file system on this drive.



How did you conclude that this machine possibly has a Fusion drive?

everymac.com does not specify if this particular iMac has the Fusion drive. Just says it is optional. So, I guess I'll have to open it up again and see what's there. If I do find the 128GB SSD, how do I use it to complete the logical volume group and get data from the HDD? Do I have to purchase an external enclosure to put it in?

Mahalo for your responses

It must be a fusion drive, and it most certainly is a 32GB rather than a 128GB SSD flash storage, you will have to rebuild the fusion drive or if you’re willing to put a SSD instead of a HDD just remove the flash and install Mac OS on the SSD

 

[Markverhyden]

How did you conclude that this machine possibly has a Fusion drive?

everymac.com does not specify if this particular iMac has the Fusion drive. Just says it is optional. So, I guess I'll have to open it up again and see what's there. If I do find the 128GB SSD, how do I use it to complete the logical volume group and get data from the HDD? Do I have to purchase an external enclosure to put it in?

Mahalo for your responses

The disk util log says the lvg spans 2 devices and you only have one. Technically someone could have used a thunderbolt drive to do this but that's way beyond what any typical user would do so the logical conclusion is FD. The good news is the old and new machine may have the same type slot so you might just be able to move the SSD over as well and the machine might just boot with both of the drives in. Obviously you need to be aware of possible data loss.

Sorry about the everymac. Could have sworn they gave as built specs if you drilled down enough but I may have been thinking of HP and Dell which do that.

 

[Haole Boy]

The disk util log says the lvg spams 2 devices and you only have one. Technically someone could have used a thunderbolt drive to do this but that's way beyond what any typical user would do so the logical conclusion is FD. The good news is the old and new machine may have the same type slot so you might just be able to move the SSD over as well and the machine might just boot with both of the drives in. Obviously you need to be aware of possible data loss.

Sorry about the everymac. Could have sworn they gave as built specs if you drilled down enough but I may have been thinking of HP and Dell which do that.

Mahalo for your response, and no worries about what everymac does or does not supply.

I was thinking that I might be able to put the HD and SSD into the 27" iMac to see if they would then work well enough so that I can create a time machine backup. But, your point about possible data loss is troubling. I've backed up the HD using ddrescue (on Linux), but how can I backup the SSD? I have not gotten back into the 21" iMac to see if there is an SSD there, but it makes sense that it would be.

Gotta do some more research before trying anything....

Harry Z

 

[Markverhyden]

Mahalo for your response, and no worries about what everymac does or does not supply.

I was thinking that I might be able to put the HD and SSD into the 27" iMac to see if they would then work well enough so that I can create a time machine backup. But, your point about possible data loss is troubling. I've backed up the HD using ddrescue (on Linux), but how can I backup the SSD? I have not gotten back into the 21" iMac to see if there is an SSD there, but it makes sense that it would be.

Gotta do some more research before trying anything....

Harry Z

Just pointing out the data loss thing. You know, CYA as the saying goes. Unlike M$ OS's you can move drives between similar models like these with a high degree of confidence of success as long as the drives themselves are OK. I've never seen one personally but I'd guess the SSD part is just standard, probably a PCIe, NVMe, etc. So I you have USB enclosures that match that you can make an image of the SSD as well. Apple creates a special type of RAID, probably some kind of striping for these. That's why @lcoughey mentioned the part about not ruining the SSD. But if there is any really important, irreplaceable data I'd look at getting a good backup first just to be on the safe side. Best of luck.

 

[Haole Boy]

Update: I just realized that I had never asked the customer if he had a backup. And, much to my surprise, he does! Look like this project is not dead yet.

And this just keeps getting better and better... just verified that the 27" iMac (the one that is working) does NOT have a Fusion drive. So, no way that I can put the HD and the SSD in it to try and create a backup. I can't find it now, but someplace I read that if the iMac does not have the Fusion Drive SSD installed from the factory there is no way to add it later.

The only alternative that I can think of to offer the customer is to send the drives to a data recovery company to have them recover the data. No idea how much this would cost.

Or, I can return the iMacs to the customer and advise him to take them to the local independent Mac store for this project.

If anyone has any other ideas, I'm listening.

Mahalo to all who took the time to respond.

Harry Z

 

[sapphirescales]

You've got two options; either run a recovery program on the image you made (I recommend R-Studio) or you can try DiskWarrior or TechTool Pro to try and see if they can "fix" the disk image. Make 100% sure that it's not a Fusion drive though otherwise you're just wasting your time. I don't think any software can recover data from a split up/corrupted Fusion drive. I don't know. I've never been in this situation.

If I get a computer in with a Fusion drive, I just transfer both drives to another Mac and back up the data manually then do a fresh install on whatever computer they choose to go with and restore their files manually. I can imagine the T2 security chip will cause a lot of problems later down the road when we start seeing them. A lot of people are going to be absolutely screwed when it comes to their data, and they're NOT going to be happy with Apple when their obsession with "security" causes them to lose all their data.

 

[Larry Sabo]

I just realized that I had never asked the customer if he had a backup. And, much to my surprise, he does!

Seems to me the solution is to restore the data from back-up to the working mac. -- unless it's really stale.

 

[Markverhyden]

Things are never easy with Apple. No surprise. I seem to remember reading that they had the SSD slot on all motherboards after a certain point. After all the cost to manufacture, maintain and track two different models for each spec, whose only difference is an SSD slot, would be very expensive. But we all know Apple does some incredibly stupid things.

If the customer is happy with the backup, as in it's recent enough for him, I'd toss in SATA SSD and call it a day. Using the built in SSD slot without an Apple SSD requires some work. So the sooner you get rid of it the better. I've always considered it to be an abomination anyways.

 

[Haole Boy]

Seems to me the solution is to restore the data from back-up to the working mac. -- unless it's really stale.

Things are never easy with Apple. No surprise. I seem to remember reading that they had the SSD slot on all motherboards after a certain point. After all the cost to manufacture, maintain and track two different models for each spec, whose only difference is an SSD slot, would be very expensive. But we all know Apple does some incredibly stupid things.

If the customer is happy with the backup, as in it's recent enough for him, I'd toss in SATA SSD and call it a day. Using the built in SSD slot without an Apple SSD requires some work. So the sooner you get rid of it the better. I've always considered it to be an abomination anyways.

Yep, that's the plan going forward. Will be picking up the backup drive later today.

Mahalo for all the suggestions!

Harry Z

 

[Haole Boy]

Have the old drive out of the 27" and am putting it all back together. Question: Can I just set the display screen in place without the adhesive strips just to make sure I've got everything back together correctly? I've removed the previous adhesive strips. I'll use masking tape to keep the screen (temporarily) in place. Good idea, or total lunacy? Don't want to wait for another set of adhesive strips to show up if I have to take it apart again.

Thanx

 

[Markverhyden]

Have the old drive out of the 27" and am putting it all back together. Question: Can I just set the display screen in place without the adhesive strips just to make sure I've got everything back together correctly? I've removed the previous adhesive strips. I'll use masking tape to keep the screen (temporarily) in place. Good idea, or total lunacy? Don't want to wait for another set of adhesive strips to show up if I have to take it apart again.

Thanx

Completely permissible, I do that on anything that needs adhesive for testing purposes. Personally I keep painters tape around for tasks like that. Never leaves any adhesive residue.