OK, we've seen step-by-step lists and articles on how to INSTALL a SQL Server 2008 Cluster, but have you run into so many issues, you feel you want to just start from scratch?  Short of rebuilding the entire server, and getting the system engineers all riled up, here are the steps to manually and cleanly UNINSTALL a SQL Server 2008 clustered instance.

Warning, some of the steps below require modifying the registry.  Be sure to back up the registry, before such an undertaking.

If SQL Server Cluster Install ends up in errors and fails, consider doing a clean up of the cluster install and then re-start it.

Uninstalling a SQL Server Instance
To completely uninstall an instance of SQL Server 2008, each node needs to be removed as part of the SQL Server failover cluster. When SQL Server is removed from the last node of the cluster, the instance and all of the SQL Server resources that are associated with it will be removed from the cluster. Physical disk resources and user data are left intact.

Here is a step-by-step process which gives a clean un-install of a SQL Server Cluster environment.

Step-1 Execute sqlrem.bat

Execute sqlrem.bat with following parameters on each node:

Syntax:

sqlrem.bat <sql install path> <instance name>

Sample:

sqlrem.bat D:\MSSQL\MSSQL$ONESQL ONESQL\ONESQL_1

Step-2 Remove Alias

Remove alias with clicnfg.exe on each node.

Step-3 Un-Install Microsoft Data Access Components

Un-install Microsoft Data Access Components from each node. This can be done using Add Remove Programs in Control panel.

Step-4 Erase Physical Directory Structure

Remove physical directory structure from each node

1. SQL Server Binary files \Program files\Microsoft SQL Server

2. Data files folder \MSSQL\MSSQL

Step-5 Remove Resources with Cluster Admin

Remove the following SQL Server resources registered with Cluster Administrator.

1. SQL IP Address

2. SQL Network Name

3. SQL Server

4. SQL Server Agent

Step-6 Registry Clean Up

Remove following registry keys if they are found:

Cluster Related:

1. HKEY_LOCAL_MACHINE\Cluster\ResourceTypes\SQL Server
2. HKEY_LOCAL_MACHINE\Cluster\ResourceTypes\SQL Server Agent

SQL Server Software Related:

1. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server

MSSQL Instance Related:

1. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ContentIndexCommon\LanguageResources\
Override\SQLServer$ONESQL_1
2. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Perflib\009
3. HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Enum\Root\LEGACY_MSSQL$ONESQL_1
4. HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Enum\Root\LEGACY_MSSQL$ONESQL_1
5. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_MSSQL$ONESQL_1
6. HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\MSSQL$ONESQL_1
7. HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\MSSQLServerADHelper
8. HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SQLAgent$ONESQL_1

Step-7 Erase the Shortcuts

1. Remove the SQL Server shortcuts in Startup menu as well as desktop.
2. Remove the Service manager entry located in startup menu.
3. Remove the Programs\ Microsoft SQL Server folder

Step-8 Restart the Cluster

Restart the Cluster Nodes one by one.

Hope this helps!