Work adventure: I/O error 21(The device is not ready )

We had an error all of a sudden on our sql server

"Microsoft OLE DB Provider for SQL Server:
I/O error 21(The device is not ready.) detected during read at offset 0x0000a7a239c000 in file 'DataFileName'.
- HY000 - HRESULT=0x80004005 “

Since the error message mentions that the drive on which one of the data file resided was not ready, it was obvious that the underlying storage was the problem.
But the System Event Log did not have any error messages related to storage. The database was online and accessible. But when I  tried accessing the Properties of this database, the same error was thrown.


The reason for this error was not something that happened at that time. Another email chain from the Windows Administrators sent a few hours ago said it all. They had found that the drive letter associated with the Mount Point hosting this data file was missing and they had *mapped* it somehow. Not sure how they had done the drive mapping. Most likely the drive hosting this data file got disconnected while the database was online.


I fixed this by bringing the database offline and back online after few seconds

ALTER DATABASE <dbname> SET OFFLINE WITH ROLLBACK IMMEDIATE
ALTER DATABASE <dbname> SET ONLINE