Bare Metal recovery allows system administrators to recover a system from failure within a short period of time and also manage system state backups in a more efficient manner. However, there is a slight catch here when you have SQL Sever binaries installed in a non-default location.

I recently worked on an issue where Windows Backup Admin was listing a non-system drive as a critical component when trying to perform a bare-metal backup using the following command:

wbadmin start backup -allcritical -backupTarget:<any existing drive name>:

When I looked into the contents of the drive, I found that the drive only had SQL Server database files and binaries on it. This is the output that I got:

wbadmin start backup -allcritical -backupTarget:S:
wbadmin 1.0 – Backup command-line tool
(C) Copyright 2004 Microsoft Corp.

Retrieving volume information…
This will back up volume OS(C:),New Disk(D:),New Disk(E:) to S:.
Do you want to start the backup operation?
[Y] Yes [N] No N

The operation ended before completion.

I then decided to use DiskShadow to show me all the critical components marked by the VSS Writers. I got the following output:

WRITER “System Writer”:

– Volumes affected by this component:

– \\?\Volume{2407f815-f9c4-11df-aef7-806e6f6e6963}\ [C:\]
– \\?\Volume{22c3ff31-f965-11df-a20b-00155df1c42a}\ [D:\]
– \\?\Volume{0342683d-f96a-11df-8a1f-00155df1c42a}\ [E:\]

This is because the SQL Server program binaries were installed on the D: and E: drives. And these are the paths that show up as critical as per the System Writer:

– d:\program files\microsoft sql server\100\dts\binn
– d:\program files\microsoft sql server\msas10.mssqlserver\olap\bin
– d:\program files\microsoft sql server\msrs10.mssqlserver\reporting services\reportserver\bin
– d:\program files\microsoft sql server\mssql10.mssqlserver\mssql\binn
– e:\program files\microsoft sql server\msas10.inst01\olap\bin
– e:\program files\microsoft sql server\msrs10.inst01\reporting services\reportserver\bin
– e:\program files\microsoft sql server\mssql10.inst01\mssql\binn

DiskShadow command used: list writers detailed

From http://msdn.microsoft.com/en-us/library/aa384630(VS.85).aspx

A volume is a critical volume if it contains system state information. The boot and system volumes are included automatically. The requester must include all volumes that contain system-critical components reported by writers, such as the volumes that contain the Active Directory. System-critical components are marked as “not selectable for backup.” In VSS, “not selectable” means “not optional.” Thus, the requester is required to back them up as part of system state.

Based on the above description, it is clear that I cannot perform a Bare Metal backup without including D: and E: drives.

Note: The above is just an example. There might be other system-critical components which are marked as not selectable for backup by other VSS Writers. VSS works on Volume Shadow concept. So, if a particular drive in a volume is marked as critical, then the entire volume would need to be backed up.

As I mentioned earlier, for system critical components, the “Is selectable: FALSE” is set (VSS_CF_NOT_SYSTEM_STATE flag is set for non-system components). In the above example, the drive on which the SQL binaries exist is marked as critical by the System Writer.