I recently purchased a SanDisk Extreme 2TB SSD to free up space on my MacBook Pro. I was gradually moving files / folders over to the SSD, which at the time would appear in the sidebar under Locations. It would appear as it’s default name, which I believe was ‘Extreme SSD’.
At some point, as I was trying to finish a uni assignment (music production) my Macbook Pro disk became full again, and so it wasn’t letting me render / complete the assignment I was working on (quite frustrating). After reviewing my disk space for options, I noticed that a decent amount of space was allocated to photos & images. As I was kind of in a rush / under pressure - I simply moved the iPhoto & PhotoBooth library(s) onto the Extreme SSD and deleted them off the laptop.
There were no immediate issues / concerns, but at some point when I went to locate a file on the SSD, I noticed it wasn’t appearing in the sidebar. After the classic - restart laptop / unplug > replug SSD (usb) - it still wasn’t showing up.
This is where I discovered the problem…
Upon opening Disk Utility > selecting Show All Devices > The Extreme SSD appeared but it was now titled ‘SanDisk Extreme 55AE Media’ with a single volume on it titled ‘APFS Physical Store disk3s1’. I’m assuming because I drag and dropped the entire app library(s) instead of the individual files / images - that the SSD was reformatted to allow compatibility between itself and the macOS (Big Sur 11.7.10).
At this point I have absolutely no idea how to access the files / folders that were relocated to the SSD, nor how to continue using it as a storage device.. since it no longer shows up as an external location in Finder.
When I try to open the Photos / iPhoto app from LaunchPad I receive this prompt (even though the Extreme SSD is plugged in):
I realise this is probably a pretty insignificant / rookie issue for some people, but if there is anyone out there who can recognise / troubleshoot the issue with me, I’d be so grateful.
When you moved your Photos and Photo Booth libraries to the SSD and deleted them from your Mac, the SSD was probably in APFS format. This format is compatible with macOS, but it can sometimes have trouble mounting automatically.
This is especially true if there’s a problem with how the volume is indexed or if macOS thinks it’s a “System” or “Container” drive.
The new name you’re seeing in Disk Utility, like SanDisk Extreme 55AE Media with APFS Physical Store disk3s1, indicates that the volume is indeed there. However, there might be a problem with the mount point, causing it to be corrupted or missing. This is why it doesn’t appear in Finder and why Photos can’t find the libraries..
To fix the issue with your SanDisk Extreme SSD not showing up, start by opening Disk Utility, choosing “Show All Devices”, and checking if the volume labeled SanDisk Extreme 55AE Media can be mounted—if so, it should appear in Finder. If not, use Terminal to run diskutil list, locate your disk (likely /dev/disk3s1), and try mounting it manually with sudo diskutil mount /dev/disk3s1.
Also, check the /Volumes directory using ls /Volumes to see if the drive is already mounted but hidden. You can open it manually from there. If mounting still fails, run First Aid in Disk Utility to repair the drive.
For the Photos app issue, hold Option while opening the app and manually select the relocated library from the SSD—once it’s mounted.
If nothing works, consider using Mac data recovery software to retrieve your files. After recovery, reformat the SSD to APFS (for Mac) or ExFAT (for cross-platform), rename it for clarity, and avoid storing system-related libraries on it in the future.
So, firstly - the SanDisk Extreme 55AE Media cannot be mounted, since it is showing a greyed out ‘Mount’ button (top right of Disk Utility) when I select it.
I followed your directions in terminal, with the results as such:
