What is this SQL Server VSS Writer Service?

If you take a look at the NT Services available in support of one or more instances of SQL Server you are likely to find SQL Server Browser, and SQL Server VSS Writer. I was really intrigued by the VSS Writer when I saw that service show up the first time years ago. At one time I thought it was the process writing changes to database objects to disk. However, if you think about it, that would be a very dangerous service to stop, which is available under NT Services. You don’t want changes to your database to be lost because the service writing them to disk is unavailable. So, what is the purpose of the VSS Writer?

The answer is quite easy. Microsoft built the capability into windows allowing files to be backed up to disk while other programs are using those files. In the old days, when we wanted to backup a SQL Server database we had two options. We either stopped the SQL Server, and backed up the database files, or, we used a SQL Server Backup call, which could be written to a file. In fact, the SQL Server Backup process had an interface allowing custom software to consume a SQL Server backup stream.

Today, the VSS Servicer interacts with the Windows Volume Shadow Copy service, allowing files that are in use, such as SQL Server data files, to be copied (or backed up) without stopping all other services accessing those files. If your server needs to backup your databases without taking the database offline, or using the SQL Server Backup Stream, then turn on the SQL Server VSS Writer service on your computer.

By default, this service is installed for all instances of SQL Server. If you have an instance of SQL Server on a machine where you are not performing file backups on your disk, you can gain minimal performance by disabling this service. Set it to startup manually in the configuration for that services.

This should be useful information for those of you having to support your small business with SQL Server installations. If your backup software is simply copying files from your disk to your backup device, be sure to turn this service on. Otherwise, set it to manual startup.