I've just reinstalled macos onto my mid 2011 iMac, and can't find my disk with 2.8TB storage in Disk Utility. So I went to terminal in recovery mode and found that there are other disks on my computer but they are not showing in Disk Utility. May I know how can I recover the 2.8TB disk? why is it not showing in disk utility.
I have attached relevant images (Disk utility & Terminal). Thank you.
iMac 27″, macOS 10.13
Your first picture shows the 3TB internal hard drive as well as a SanDisk SSD. Your second picture with the command line shows the SSD is 128GB, but it does not show the SSD as properly partitioned & formatted so I suspect you have a broken Fusion Drive setup. The command line also shows some odd partition layouts on the hard drive which includes 16MB Microsoft partition.
This first thing I would do is verify the health of the internal hard drive by running the Apple Diagnostics. If you can boot into the full macOS (either internally or externally), then you can run DriveDx to check the health of the hard drive (post the DriveDx report here using the "Additional Text" icon which looks like a piece of paper). Usually a "Warning" or "Failing" notice indicates a worn out hard drive or a physically failing hard drive. Both conditions mean the hard drive should no longer be used.
You should make sure you have a good backup while you can still access the data on the hard drive since you will need to reset the Fusion Drive which will destroy all data on both the SSD and the hard drive.
How to fix a split Fusion Drive - Apple Support
You should always have frequent and regular backups of your computer and all external media which contains important & unique data.
Your first picture shows the 3TB internal hard drive as well as a SanDisk SSD. Your second picture with the command line shows the SSD is 128GB, but it does not show the SSD as properly partitioned & formatted so I suspect you have a broken Fusion Drive setup. The command line also shows some odd partition layouts on the hard drive which includes 16MB Microsoft partition.
This first thing I would do is verify the health of the internal hard drive by running the Apple Diagnostics. If you can boot into the full macOS (either internally or externally), then you can run DriveDx to check the health of the hard drive (post the DriveDx report here using the "Additional Text" icon which looks like a piece of paper). Usually a "Warning" or "Failing" notice indicates a worn out hard drive or a physically failing hard drive. Both conditions mean the hard drive should no longer be used.
You should make sure you have a good backup while you can still access the data on the hard drive since you will need to reset the Fusion Drive which will destroy all data on both the SSD and the hard drive.
How to fix a split Fusion Drive - Apple Support
You should always have frequent and regular backups of your computer and all external media which contains important & unique data.
I followed your instructions, first running Apple Diagnostics (imaged attached below) and ran DriveDx (DriveDx report posted in "Additional Text"), may I know if you could advise on my next step?
I have previously tried to use BootCamp to download windows on one of my partitions but failed, which might be why my drive is messed up now. I still have 2.8TB of important data in my drive, is it possible for me to recover the data? How can I backup the data now?
Thank you for your help.
I believe the hard drive is still healthy although its overall health is down to about 42% now. The drive does have four High Fly Writes, but I don't think that would cause your problem here. It should be safe to attempt data recovery.
You can try using a data recovery app such as Data Rescue. I've seen some mention of Stellar Data Recovery, but I've never used it. I have not used Data Rescue in many many years so I forget exactly how the app works on a drive like yours which is missing a whole partition. Depending on what happened, you may have to sort through thousands of unnamed files. However, you will need to have a bootable macOS drive with a full version of macOS so you can run the data recovery app on the internal hard drive. If you don't already have such a drive, then you can install macOS to an external USB drive.
If I were to recover the 2.8 TB of data, does it mean I have to free up more than 2.8 TB of space in the bootable macOS drive or external USB drive to recover the data?
You have to have somewhere to store the data since you cannot store it on the drive you are recovering data from. Just make sure to keep at least 20GB of storage free on the macOS boot drives.
How to recover a hidden disk in High Sierra (mid 2011 iMac)?
