# Saturday, 24 March 2007

Does your backup and recovery strategy take the new SQL Server 2005 mssqlsystemresource database into account? What's different for SQL Server 2000 and 2005 from backup/restore perspective.

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Compared to SQL Server 2000, SQL Server 2005 has a lot of nice features aimed at minimizing downtime during "unplanned events", most notably piecemeal restore and the inclusion of Full-Text indexes in the database backup and restore. However, before being able to do database restores, a functional database server is needed. Besides being a SQL Server instance, the database server also is at least a Windows operating system and hardware (or a virtual machine if you like). The later two usually are the domain of the system administrator who will also take care of the operating systems, including installed applications, being backed up. Likewise the DBA will take care of databases.

A typical system backup will exclude certain files and directories known to be always locked, like pagefile.sys and the SQL Server \Data folder. The other SQL Server folders and registry-setting (system state), are backed up. By restoring this backup for a SQL Server 2000, you get a database server with the Service Pack level of at time of the backup. The only thing that's missing for the database to start is the master database. In SQL Server 2005 only the master database isn't enough to get you started, you need mssqlsystemresource a.k.a. Resource Database as well.

What has changed that this is an important issue in the last step of getting a SQL Server instance running (quickly). The master database in SQL Server 2000 holds all information, the configuration related to the instance (like; logins, linked servers, databases) and the definition of system objects. When applying a service pack, typically maintenance on the system object is done, so the master database changes and is therefor Service Pack dependant. In SQL Server 2005 these two types of information are split, instance configuration still goes into the master database, but the system objects are held in the Resource Database. The advantage is that master is not depending on the Service Pack and since none but Microsoft should alter system objects, the Resource Database can remain read-only and will only be changed by Microsoft when applying the Service Pack.

When disaster strikes the (original) server, in many cases, a restore of the file system and system-state is performed on a more or less comparable machine configuration. This is the quick route, compared to installing Windows, a new instance and applying the Service Pack. The quick route has two extra advantages, no access to installation media is needed and other applications are restored too. But the quick restore route does not bring back a fully functional server, both sysadmin and DBA are aware of that. Therefor for this procedure to be successful, an offline backup of master (copy master.mdf and mastlog.ldf) was done after installation and application of a Service Pack. Now the last step is to copy master.mdf and mastlog.ldf to the SQL Server \Data folder. From here the DBA can start his/her database restore sequence (starting with the latest online backup of master (2000/2005)). This approach works on SQL Server 2000.
For SQL Server 2005, you have to add include the Resource Database in this strategy. And here is a little (positive) difference, because the Resource Database is accessed read-only, it only has read locks and thus can be copied while the instance is running. So you can either copy it after the installation or when the Service Pack is applied, or you can alter the file system backup to specifically include the files mssqlsystemresource.mdf and mssqlsystemresource.ldf.

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What if disaster struck your SQL Server 2005 instance and you haven't cared for the Resource Database... well then you're off to the slow route of installing the instance after the restore and applying the Service Pack, before the database restore sequence can be started.