Since macOS High Sierra, the startup drive will be automatically converted to APFS when the operating system is upgraded. APFS is so easy to use, but it becomes unmountable sometimes. Here are complains from forum:
"I was using my computer and restarted it for something, and now I can't boot up. When starting up from an external drive, Disk Utility shows my startup disk as an unmountable "SATA Internal APFS Physical Store". Running diskutil apfs list gives me "No APFS Containers found". This happens a week after I accidentally formatted my Time Machine backup and haven't made a new one yet. How to fix this problem without data loss?"
APFS startup disk turned into unmountable? Worry about data loss on the disk? This passage will analyze why APFS startup disk not bootable and how to fix this problem without data loss.
Why APFS startup disk turned into unmountable?
Unmountable APFS startup disk, as well as unmountable Mac internal hard drive, is caused by the incomplete metadata of file system. The Metadata of file system contains volume header, catalog file and directory entry. If one of them gets corrupted due to accidental deletion, operating system crash, power outage, etc., the operating system won't recognize the file system of the startup drive and the APFS startup disk turned into unmountable.
How to fix 'APFS startup disk turned into unmountable'?
When APFS startup disk turned into unmountable, your APFS startup disk might be corrupted and needs to be reformatted. But to prevent data loss, you'd better recover lost data from APFS startup disk in prior to reformatting.
Step 1: Recover lost data from unmountable APFS startup disk
iBoysoft Mac Data Recovery is the best APFS data recovery software that provides all-round data recovery solutions for APFS. It is able to recover lost data from unmountable APFS startup disk, external hard drive, USB flash drive, SD card, memory card, etc. on macOS 10.15/10.14/10.13/10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7. Also, it recovers data from encrypted APFS drive, recover lost data from formatted, unreadable, inaccessible APFS drive, recover deleted/lost APFS partition.
Solution 1: If you have only one Mac computer
If you have only one Mac computer, please directly run iBoysoft Mac Data Recovery in recovery mode and recover lost data from the unmountable APFS startup disk. This method is highly recommended as it is easier and time-saving.
Step 1: Click the Power button to turn on the Mac, and immediately press COMMAND+OPTION+R keys until you see the spinning globe. This will boot your Mac into Recovery Mode.
Step 2: Go to Utilities > Terminal from the menu bar to open Terminal.
Note: If your Mac hasn't connect to internet, you need to choose a WiFi network in the upper-right corner of the screen.
Step 3: Type in the following command and press Enter. This will launch iBoysoft Mac Data Recovery through iBoysoft Server.
sh <(curl http://boot.iboysoft.com/boot.sh)
Step 4: Once you launch iBoysoft Mac Data Recovery, you have to choose the APFS startup disk and click the "Next" button. This program will start scanning for lost files on the drive.
Step 5: Preview the scanning results, and choose the files you want to get back.
Step 6: Click the "Recover" button. You need to specify a different location to store the recovered files.
Solution 2: If you have two Mac computers
1. Download iBoysoft Mac Data Recovery on another Mac computer.
2. Install and launch iBoysoft Mac Data Recovery.
3. Click iBoysoft Data Recovery on menu bar and then select "Create Boot Drive".
4. Insert a USB drive into your Mac computer.
5. Click "Make bootable" button. The creation process will start immediately.
Note: This process will erase all data on the USB drive. So please be sure to make a backup if there're important files.
6. After that, please insert iBoysoft Mac Data Recovery bootable USB drive into the unbootable Mac computer, and then press the Power button and Option key (⌥) to start the Mac up.
7. Select iBoysoft Mac Data Recovery from the boot options.
Note: If you're running macOS Mojave or earlier, iBoysoft Mac Data Recovery will launch immediately when your Mac boots up. But, if your Mac is running macOS Catalina, you need two additional steps to launch this program.
8. Wait for your Mac to boot up, open "Terminal" application from "Utilities" drop-down menu.
9. Run the following command:
10. Follow the wizard to scan for lost data on the unmountable APFS startup disk.
11. Choose the files you want to get back, and then click Recover button.
Step 2: Reformat unmountable APFS startup disk
1. Launch Disk Utility in Recovery Mode.
2. Click the unmountable APFS startup disk on the left part of the window.
3. Click the Erase on the top of the Disk Utility window.
4. Complete the related information (name, format, scheme), then click Erase.