SQL Server Error 21 – The operating system returned error 21(The device is not ready)

Error Description:

The operating system returned error 21(The device is not ready) Databases not accessible after restart.  The following error is popped up every time restart Windows operating system is done :

Error 21 was returned by the operating system.(The device is not yet operational.) or
sql server drop database error 21 or
the operating system returned error 21(failed to retrieve text for this error. reason: 15105) or
sql server error: 21, encryption not supported on the client

you will see that running chkdsk /r on the disc and found no bad sectors.
DBCC CHECKDB and you will not found errors.

DBCC CHECKDB discovered 0 allocation and 0 consistency errors in the database

But When you restart SQL Server Services, the errors go away.
SQL Server 2016 Express and above on Operating systems 2012 upwards and Windows 10.

Solution:

This is due to a disk being offline or not being online either at the time SQL Server started, or had transitioned states after SQL Server has been online.

ms sql server error 21  or the operating system returned error 1006 error is normally related to disc issues.

severity 20 error sql server is another error related.

Additionally, ensure that any disc filter drivers for things like anti-virus, host intrusion protections, and so on are up to date, as these may also be blocking the service/startup/state

Most likely the problem is due to “Fast startup” power options.

It is a Windows technique to reduce the boot time called “Fast Startup” combines elements of a cold shutdown and the hibernate feature.

You can disabled it and the problem can be resolved in Windows 10.

error 21: the device is not ready windows search is another error encountered
dbcc checkdb would not work or give any consistency errors