Error 823: I/O error detected

 Error 823 is a severe I/O error that usually indicates a problem with your SQL Server's disk subsystem. This error can be caused by hardware issues, driver problems, or disk corruption. Here are some steps to troubleshoot and resolve this issue:

1. Check the Event Logs:

   • Review the Windows Event Viewer logs for any disk-related errors or warnings. Look for any messages related to hardware failures or disk I/O errors.

2. Run DBCC CHECKDB:

   • Use the DBCC CHECKDB command to check the integrity of your databases. This command can help identify and sometimes repair database corruption.

     DBCC CHECKDB (YourDatabaseName) WITH NO_INFOMSGS, ALL_ERRORMSGS;

3. Check Disk Space and Health:

   • Ensure that there is enough free space on the disks where your database files are stored.
   • Run disk diagnostics tools (such as chkdsk) to check for disk errors or bad sectors.

4. Update Drivers and Firmware:

   • Make sure that all disk-related drivers and firmware are up to date. This includes drivers for your RAID controller, storage controller, and any related hardware.

5. Review SQL Server Logs:

   • Examine the SQL Server error logs for any additional information or patterns that could help identify the cause of the error.

6. Backup and Restore:

   • If the database is severely corrupted, consider restoring from a recent backup. Ensure that your backups are valid and tested regularly.

7. Consult with Your Hardware Vendor:

   • If you suspect a hardware issue, contact your hardware vendor for support. They may be able to provide tools or diagnostics to help identify and resolve the problem.

8. Check for Updates:

   • Ensure that your SQL Server instance is running the latest service pack or cumulative update, as these updates often contain fixes for known issues.

If the error persists after following these steps, you might need to involve your database administrator or a SQL Server expert to perform a deeper investigation and resolution.

Logon failed due to trigger execution

 The error "Logon failed due to trigger execution" occurs when a logon trigger in SQL Server prevents a user from logging in. Logon triggers are special stored procedures that execute in response to a LOGON event, and they can be used to enforce security policies, restrict access, or log login activity.

Steps to Resolve the Issue

1. Identify the Logon Trigger:

• Determine which logon trigger is causing the issue by querying the system catalog.

SELECT name, create_date, modify_date, is_disabled
FROM sys.server_triggers
WHERE type = 'TR' AND parent_class_desc = 'SERVER';

Check the Trigger Definition:

• Check the code of the logon trigger to understand its logic and why it might be causing the logon to fail.

-- Check the trigger defination
EXEC sp_helptext 'TriggerName';

Disable the Trigger (If Appropriate):

• If the trigger is incorrectly preventing logons, you can disable it.

-- Disable the trigger
DISABLE TRIGGER TriggerName ON ALL SERVER;

Fix the Trigger Logic (If Needed):

• If the trigger logic needs adjustment, modify the trigger code accordingly.

ALTER TRIGGER TriggerName ON ALL SERVER
FOR LOGON
AS
BEGIN
    -- Your trigger logic here
END;

Re-enable the Trigger:

• After fixing the issue, re-enable the trigger.

ENABLE TRIGGER TriggerName ON ALL SERVER;

Example Scenario and Solutions

Scenario: A Logon Trigger Prevents All Logins

Problematic Trigger:

CREATE TRIGGER PreventLogons
ON ALL SERVER
FOR LOGON
AS
BEGIN
    ROLLBACK;
END;

This trigger prevents all logons by rolling back every login attempt.

Solution:

1. Disable the Trigger:

DISABLE TRIGGER PreventLogons ON ALL SERVER;

Modify the Trigger Logic (e.g., to allow logins during business hours):

ALTER TRIGGER PreventLogons ON ALL SERVER
FOR LOGON
AS
BEGIN
    IF DATEPART(HOUR, GETDATE()) NOT BETWEEN 9 AND 17
    BEGIN
        ROLLBACK;
    END;
END;

Re-enable the Trigger:

ENABLE TRIGGER PreventLogons ON ALL SERVER;

Practical Steps to Diagnose and Fix the Issue

1. Identify Active Logon Triggers:

SELECT name, create_date, modify_date, is_disabled
FROM sys.server_triggers
WHERE type = 'TR' AND parent_class_desc = 'SERVER';

Review Trigger Definition:

-- Replace 'TriggerName' with the name of the trigger
EXEC sp_helptext 'TriggerName';

Disable the Trigger:

-- Replace 'TriggerName' with the name of the trigger
DISABLE TRIGGER TriggerName ON ALL SERVER;

Fix or Adjust the Trigger Logic:

ALTER TRIGGER TriggerName ON ALL SERVER
FOR LOGON
AS
BEGIN
    -- Adjust the logic to prevent inappropriate logon failures
END;

Re-enable the Trigger:

ENABLE TRIGGER TriggerName ON ALL SERVER;

By following these steps, you can diagnose and resolve issues related to logon triggers preventing successful logins