I have a SSD that has gone bad. Many files have non readable areas. They don't return corrupt data; they cause a long delay in read retries and then the read fail. Samsung magician returns some bad numbers in S.M.A.R.T. But why does windows not warn me the drive has gone bad? Scanning the drive with Magician shows many bad sectors, but doing a disk scan in windows shows no error.
The BIOS should have S.M.A.R.T. enabled to detect bad sectors in HDDs and is enables by default as far as I know... but since SSDs are not supposed to have sectors, it may be the reason you hadn't noticed the problem. Windows has the CHKDSK tool that detects bad sectors from the moment the OS starts loading, and offers doing the the scan... but if SSDs don't have sectors, it may be the reason the problem went unnoticed. But you can run chkdsk manually to make file system corrections and repair "bad sectors", which information says are present in SSDs in a lower number. Your alternatives are to run chkdsk to detect bad sectors and repair them and to find and repair file system errors. If will do what it can do, and not find what it can't.
CKDSK alternatives
Unlike HDDs,
SSDs do not have a built-in mechanism to detect and repair bad sectors. Therefore, you need to use third-party tools or utilities to scan and fix your drive. Some examples are CHKDSK, S.M.A.R.T., CrystalDiskInfo, and SSD Toolbox.
If you don't want to use third party software to check the SSD, this may help
A second search says:
"How to use chkdsk for SSD?
Select Troubleshoot > Advanced options > Command Prompt. Type CHKDSK /f in the elevated command prompt and hit Enter. Wait for the CHKDSK utility to complete the scan, then type Exit and hit Enter."