Not reading anymore external Sandisk SSDs

See if your SanDisk external SSDs have a firmware update available. There is a known issue with some of the Sandisk external SSDs including data loss (although the latter has never been admitted by Western Digital).

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

News articles about the issue (there are more):

https://arstechnica.com/gadgets/2023/08/sandisk-extreme-ssds-are-still-wiping-data-after-firmware-fix-users-say/

https://arstechnica.com/gadgets/2023/08/sandisk-extreme-ssds-are-worthless-multiple-lawsuits-against-wd-say/

Make sure to connect the drive directly to the computer and disconnect all other external devices in case one of them has a problem. Also try using another cable. If you need to use an adapter, then try another adapter as well.

Try connecting the external SSD to another USB-C port......if a laptop, then connect it to the port on the other side of the laptop.

Try booting into Safe Mode to see if that makes any difference. Doubtful this option will make a difference, but it never hurts to try. If this works, then it may indicate an issue with some third party installed software, or it may just be coincidence where the SSD hardware failure "fixed" itself (perhaps just temporarily).

If you run DriveDx (free trial period) as suggested by @Grant, then post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.

in your first screenshot, attempting to erase the device caused "I/O error". Although that sounds generic, it is actually VERY specific. It says that after 1000 re-tries, the drive controller was unable to obtain clean data for a data block. Since the only blocks re-written during an ERASE operation are in the Directory area, this drive has a Bad Block in the Directory area. it may not be useable.

Generally speaking, ALL drives carry a finite private stash of spare blocks that can be substituted for blocks found BAD. So we would expect a spare block to be substituted and the process to succeed on next try, because NEW data are available on next try.

When Erasing, the drive must respond correctly as its full-rated SIZE. During the ERASE process, the FIRST and LAST blocks are also written. If the drive has consumed ALL its spare blocks, it can no longer write the last (highest-numbered) block. In that case, it FAILS Erase, and can no longer be used for this purpose.

The inexpensive third-party Utility DriveDx can provide additional insights into errors, spares, and drive life remaining.

Note: Obtaining this information from External devices sometimes requires a free add-on utility, details inside DriveDx.

01x01 wrote:

• My MBP M1 Max is not reading USB SSDs anymore, in particular Sandisk Extreme SSDs.

I tried with multiple SSDs from Sandisk and all of them fail to mount or being initialised. They are completely useless and sometimes Disk Utility struggles to recognize the device.

I tried the SSDs on other Macbooks and they works as should, so the problem is not the drives, but something on my PC.

I get different kind of errors, some of them are:

Couldn’t open device. : (-69877)

POSIX reports: The operation couldn't be completed. Input/output error. : (5)

Troubleshooting:

In Activity Monitor there is no `fsck_xxxx` process.

• First Aid in Disk Utility says that is all good.

• These errors happen also in recovery mode.

• Issue is not the USB cable.

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

DiskUtilility>View>Show All Device

verify the Parent Drive, Containers, Volumes. If errors are found run it again until no errors reported.

If no resolve I would replace the drive.