File System Rights Needed to Attach a Downgrade DB

This falls into the category of things I probably should have already known, but for some number of reasons (not all my fault!), I didn’t.

Last Thursday night was an honorary Friday night at The Hideaway, since we took last Friday off (I got screwed at work on a day of for New Year’s this year), so I was trying to catch up on some blog posts in my reader. One of them included some code I wanted to run, but I found out that I didn’t have AdventureWorks attached to SQL after the last rebuild of the main server at home. The first step was going to be fixing that, so I moved the files from their old location to my new standard folder and set off to Attach…

Before this story gets too long…

The DB wouldn’t attach to the SQL 2008 instance. I was using my old SQL 2005 version of AdventureWorks, because it was already on the machine and at least for now, I want to keep it around. It was complaining about the files or the DB being set to Read-Only, and it can’t do an upgrade on a Read-Only DB. I needed to fix the DB or the file system permissions.

The DB wasn’t read-only when I killed the server before the rebuild, so that wasn’t it. Had to be NTFS permissions.

Checked those and the group that the SQL Service Account had Modify permissions on the folder where the files were. Checked this a few times to make sure I wasn’t crazy. I tried to search out some help on this, but I was having a hard time getting the search terms right to find anything useful. I finally wound up breaking out ProcessMonitor to help figure out what was going on.

Turns out, SQL Server was using (impersonating?) the Windows account I had connected to the instance with when it was reading the files. That account doesn’t have write access to the folder(s) in question, so any writes it was trying to do were failing. That’ll do it.

I don’t understand why it does this. Nothing is mentioned in BOL about this, and some real quick Googling didn’t bring up anything, either. Since I pretty much work only with SQL 2000 and SQL auth all day right now, I don’t know if this is new in 2008. At my last job where I had 2005, whenever I would do an operation like this, my Windows account would have been Local Admin on the server, so I wouldn’t have run into it.

I did some quick testing and although it of course still impersonates the Windows Auth user when you attach a DB that doesn’t need upgrading, as long as the user you’re logged on with has read rights, you’ll still be in business.

Workaround(s)

Obviously giving write rights to the Windows account you’re logging on to SQL with will fix this, but that doesn’t strike me as a good idea if you don’t have those rights in the first place. I mean, you don’t have those rights for a reason, right (principle of least privilege, etc)? But, if it’s a Windows Auth-only situation, that’s the only way to do it with the account in question.

Another way around it, is to use SQL Auth. This is what I wound up doing, mainly because I wanted to test to see if that works. As mentioned, if the Instance isn’t in Mixed Mode Auth, this isn’t an option. Also if, for whatever reason, creating a new account for this purpose isn’t allowed, then this option also doesn’t help you.

I’m sure this is old news to most everyone else, but it caught me by surprise. Lesson learned!

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