Why is my external SSD taking so long to load on MacBook Pro Disk Utility?

You can run DriveDx (free trial period) to check the health of the drive. You will need to install a special USB driver in order to attempt accessing the health information on the external drive. Post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.

Have you tried running Disk Utility First Aid on the external drive? You will want to run First Aid on the whole physical drive, then on the hidden Container if using the APFS file system on it, otherwise run First Aid on each item on the external drive in order. Even if the First Aid summary says everything is "Ok", click "Show Details" and scroll back through the report to see if any unfixed errors are listed. If there are errors, then run First Aid again until they are gone. If after several scans the errors remain, then they cannot be fixed. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drive & hidden Containers appear on the left pane of Disk Utility.

What file system is on this external drive?

Is the drive connected directly to the computer?

Have you tried using another USB cable?

Make sure to disconnect all other external devices in case one of them is causing a problem.

If First Aid cannot repair the file system, then I guess you could try repairing the exFAT file system by using a Windows computer to see if that makes any difference.

If the file system cannot repaired after several attempts, then @The_Knowledge_Seeker is correct.....you will need to erase the whole physical SSD followed by restoring from a backup assuming the SSD is healthy.

STTRUKII wrote:

I do not want to reformat the drive as I need it immediately and cannot spend days backing up and redownloading content.

If you don't have a backup of your external drive and that drive contains important data, then that data is at severe risk of being lost. Backing up that data should be priority number one.

STTRUKII wrote:

I installed DriveDx and while it initially recognised the drive and told me to install a driver once the driver was installed the drive stopped showing up.

Are you saying DriveDx could not access the health information on the SanDisk SSD even with its third party USB driver installed?

I have seen cases where the drive manufacturer's proprietary software may not be compatible with the special USB driver that DriveDx provides. I believe it was the Samsung software, but I guess others could be similarly affected. If that special USB driver is preventing the SanDisk SSD from operating correctly, then you can uninstall that special USB driver that DriveDx installed by using the instructions in the following link:

https://binaryfruit.com/drivedx/usb-drive-support#:~:text=uninstall%20instructions

The software is working as it recognises other HDD drives I have. The drive is formatted exFAT and running First Aid gets stuck on Checking system hierarchy for hours. I also get this error in terminal

File system errors can easily cause all your problems. It is also possible a hardware issue caused the file system errors.

You may also want to check to see whether your SanDisk SSD has any firmware updates available since some SanDisk Extreme SSDs are known to have serious firmware issues that can result in data corrupt and even data loss although the WD/SanDisk firmware page neglects to mention the data loss part.

https://support-en.wd.com/app/firmwareupdate

Here is an article regarding the SanDisk Extreme SSD firmware issues & data loss:

https://arstechnica.com/gadgets/2023/05/sandisk-extreme-ssds-keep-abruptly-failing-firmware-fix-for-only-some-promised/

It sounds as though you need to erase the external drive but I appreciate you said you didn't want to do this. Do you have a Time Machine backup in place? (I'm assuming the external drive is not a Time Machine drive as you said you needed to use it immediately.) And, if so, is there a backup of your external drive as well as your internal drive? If there is, then you can erase the drive and migrate / copy your data back onto it from your backup.

There is a possibility that your external drive is beginning to fail mechanically, in which case you urgently need to back it up in any event if you don't already do so as a matter of course, or you will irrecoverably lose all the data on it when it fails.

In order to perform a low level block clone you should be booted from an external drive. There is no way you can clone the same drive you are booting since the data will be constantly changing which would lead to an unreadable clone (or files will be broken).

I've never had to clone a bad SSD before since that is highly unusual. It would help to have the complete DriveDx text report to review in order to try to understand the issue with the SSD. I prefer the DriveDx text report since it provides the information needed in a format that is easier to read than what most other drive health monitoring apps provide. I can try to read the Disk Drill health report, but IIRC it wasn't very useful the last time I saw one posted on this forum.

I've never used Disk Drill so I'm not sure how any of its various components work. I do know that most apps are not able to handle the errors of a failing drive.

I hope going forward you will be including your external media in your backups.

FYI, you should make sure to erase the SSD before sending it to SanDisk so that your data cannot be accessed.