Hi, I have a CT500MX500 (firmware M3CR045) as cache drive, and it randomly had read/write errors, but as soon as I reboot and repair with btrfs it works fine for a few days (until the same happens). I figured its just dead and popped in a new drive.

I pulled all the data from the btrfs pool and threw the disk into my Windows pc, where I'm doing a full scan, but everything looks fine.
Furthermore, I read about firmware issues that randomly causes it to be stuck (which would kinda fit?) can I update the drive firmware on Windows and throw it back into unraid?
Or should I just write it off and forget the 40€, or can I just update the firmware on Windows?
Sadly didnt create a diagnostic zip when it happens, but generally the drive was just unresponsive and after reboot btrfs managed to fix all issues as it was a mirror

 

Try updating the firmware, it's been reported to help:

https://forums.unraid.net/topic/134954-warning-crucial-mx500-ssds-world-of-pain-stay-away-from-these/?do=findComment&comment=1255816

 

so updating via windows is fine?
Its actually updating the firmware on the ssd and not just some driver?

Yes and it's updating the device firmware.