Help Can't write to SD card

[MotoE5isBest]

Until very recently my SD card has worked fine but now it cannot have data be written to it. I have tried on both the device and on my computer. I can still read all the data on it. I'm running on Android 8 (Oreo). I have recently renamed the drive, it's formatted as internal storage.

 

[mikedt]

So both your computer and phone can't write data to it? Could be it's failed and gone read only? Or the file system has corrupted?

Going read only is something micro-SDs can do when they have a problem, basically to try and preserve the data on them. Micro-SDs can and do wear out, as flash memory only has a finite number of write cycles. How long have you had it? You could try reformatting it.

 

[MotoE5isBest]

Sorry for the (slightly) belated response.
My computer and phone can not write to the SD card.
I don't know if it's failed and gone into read-only mode, is there a way I can check? As for how long I've had it, nearly a year but it's a 128GB card and I still have 50ish GB free and have never filled up that space.
What would reformating it do?

 

[mikedt]

Copy everything off the micro-SD first, if you haven't already made a backup of it. Formatting will erase erase everything, and reinitialise the file system as if it was new. However if the format doesn't work because it failed read only. You'll need to replace it. Check if it's still under warranty?

As I posted previously, micro-SDs can and do fail, mainly because they have a finite number of write cycles. They can literally wear out.

 

[Cao Van Thanh]

You need to backup your data and format your sd

 

[svim]

.... it's formatted as internal storage.

Once any microSD card has been reformatted as 'internal' (a.k.a. 'adoptable') it's fundamentally changed in at least two significant ways -- its file system is changed to ext4 and its encrypted. You cannot expect to use an 'internal' card the same as a 'portable' card. Once internal, its meant to be left in your phone at all times, it's basically been altered to be another internal component. The Android OS on your phone sees an internally formatted card as just an added storage memory to the actual internal storage media in your phone. It's the installed Android OS that manages everything on that card at that point, your direct interactivity is very limited now. You can do some file management using your phone's Settings >> Storage menu to the now internal card, but a file manager app no longer sees an internal card as a separate storage media volume.
By default microSD cards are formatted with Microsoft's FAT file system (either FAT32 or exFAT depending on the card capacity size). Most operating systems (Windows, MacOS/OS X, Linux, Android, etc.) include basic FAT support so microSD cards are considered to be (more or less) universally transferable between platforms -- you can use a card to move files between say a GoPro camera to a WinPC to your phone. But once you formatted the card from its default 'portable' status to 'internal' that changes everything. Once internal its now ext4, the same file system as your phone's internal storage (so both your phone's internal storage media and your microSD card are the same). and its encrypted with the storage key tying it directly and only to your phone (so the contents of the card is fully accessible only on your phone and by your phone's OS, which is why you can have limited file management using just the Settings menu but not a third-party file manager app).
If you want to have your card transferable and removable again you need to reformat it back to 'Portable' again. Just be sure to back up what you can (again, using your phone's Settings >> Storage menu).