未安装sql server 2005 vss writer服务。我该如何解决？

I attempted to update sql server 2005 with SP2. I get a failure due to not starting vss writer. When I go into services, I see that vss writer is not installed. (not even listed in services). When I check my other redundant servers, I see that vss writer service is installed. How do I add the service?I attempted to update sql server 2005 with SP2.