There are 2 types of errors. Logical errors and physical errors.
Lots can be done to address logical errors.
Not much can be done to address physical errors - besides RAID (not RAID0) and good backups.
Sometimes the best solution for RAID issues is to destroy the array, recreate it and restore the data from backups. RAID never replaces backups. RAID solves 2 problems. Backups solve 999 problems, and I'm not exaggerating.
So, first, let's get an overview of your storage. Run these 2 command and post the command + output back here. Use forum code tags or it will be too hard to read (i.e. I won't read it).
Code:
df -hT -x squashfs -x tmpfs -x devtmpfs
lsblk -e 7 -o name,type,fstype,size,FSAVAIL,FSUSE%,label,mountpoint
If the setup uses LVM, you should also run and post these commands:
Code:
sudo pvs
sudo vgs
sudo lvs
If BTRFS or ZFS are involved, I can't help, but you need to be clear about that.
After we see that output, next steps can happen.
I don't need descriptions of the output.
For logical errors, the first step is to run an fsck on the unmount file system device. The device for the file system will be in the output requested above. Many issues can be solved by that.
BTW, you have looked at the system logs already, right?