When we are working with MS SQL Server databases, we are getting the following error in some of the SQL Server instances. Msg 823, Level 24, State 2, Line 2 The operating system returned error 21(The device is not ready.) to SQL Server during a read at offset 0x00000000056000 in file 'E:\SQLDEV22\databasefiles\crystalspidersinst_0700.mdf'. Additional messages in the SQL Server error log and operating system error log may provide more detail. This is a severe system-level error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online. This is one of the major issue at Microsoft SQL Server storage-level. Quick Remedy: Restart the SQL Server service The error means SQL Server is trying to read the MDF file from disk E: but Windows unable to access the disk/device properly. The reasons are as follows: The drive may be disconnected External HDD/SSD failure Disk has corruption VM mounted disk issue Storage controller issue Bad sectors Antivirus or any other software locked the file Let's start step by step troubleshoot: Step 1 — Check the Windows Disk Open Command Prompt as Administrator, run the following command to check and repair the bad sectors. I am assuming it is E: drive has database files. /> chkdsk E: /f /r Step 2 — Run DBCC CHECKDB command If the database is online, then run the following command. Replace the database name with your actual database name. DBCC CHECKDB ('YourDatabaseName') WITH NO_INFOMSGS, ALL_ERRORMSGS; If the database is in SUSPECT state, then run the following commands. ALTER DATABASE YourDatabaseName SET EMERGENCY; ALTER DATABASE YourDatabaseName SET SINGLE_USER; DBCC CHECKDB ('YourDatabaseName', REPAIR_ALLOW_DATA_LOSS); ALTER DATABASE YourDatabaseName SET MULTI_USER; Thank you