How to Move a Mirrored Database MDF and LDF Files?

Couple of days ago, I had a conversation with one of my colleagues, on how to move database files from one location to another which is has DB Mirroring enabled. In this blog post, let’s see that in action..

Let’s consider the below Scenario:

1. You’ve a Large Database(let’s say 500+ GB DB) which is participating in DB Mirroring as a ‘Principal’ Database.

2. That’s the only database sitting on this Instance, a Dedicated Instance for your Application(In other words, detaching-attaching DB will cause almost the same impact as SQL Services Restart)

3. You want to Move your MDF and LDF files to another LUN (because of space constraints or you are doing SAN Expansion or something else)

4. You do not want to Break Mirroring completely, because you do not want to re-configure everything from scratch…which takes considerable amt. of time and not acceptable to your Business, running without DR for that long period of time.

5. What is the option we have in this case?

Solution: First thing to note, we can’t detach a Database while it is participating in Database Mirroring. You’ll get the below error if you try to do so..

“The operation cannot be performed on database “Mirror_tst” because it is involved in a database mirroring session.
ALTER DATABASE statement failed.”

so what to do now..? Remember, we’ve ALTER DATABASE…..MODIFY FILE….to do this trick.

Demo:

I’ve a database called ‘Mirror_tst’ which is being mirrored from PROD Instance to DR Instance as you can see below. Also, please note the current database file locations in the below screenshot(As of now, they are in default location)

Now, Let’s update the database file(s) location in system catalogs to “C:\Backs\” folder. For this I’ll issue the below commands.

ALTER DATABASE mirror_tst
MODIFY FILE(NAME= mirror_tst,FILENAME=’C:\Backs\mirror_tst.mdf’)
GO
ALTER DATABASE mirror_tst
MODIFY FILE(NAME= mirror_tst_log, FILENAME= ‘C:\Backs\Mirror_tst_log.ldf’)
GO

and i received below messages:

The file “mirror_tst” has been modified in the system catalog. The new path will be used the next time the database is started.
The file “mirror_tst_log” has been modified in the system catalog. The new path will be used the next time the database is started.

So, the database file locations were modified in system catalog, all we have to do now is Stop SQL Service, move the physical files and start SQL Services. Let me do that!

I issued SHUTDOWN WITH NOWAIT on my PRINCIPAL Server as you can see below.( Be very cautious with this statement, understand what exactly you are doing before running this statement on your Prod Instance, believe me guys, Running this single statement unknowingly might cost you, loosing your Job!!..)

 

As you can see SQL is stopped and now, I moved the Physical files to ‘C:\Backs” folder as you can see below.

Now, I’m starting SQL Services and let’s see what happens to our database and more importantly to our Mirroring Status, keeping my fingers crossed 🙂

Once Restarted, the SQL Server was happy to bring up this Mirrored Database and our Mirroring Process is running happily without any issues as you can see below:) 🙂 Notice Physical files new location and the Mirroring Status now. Everything is pretty Normal:)

Hope this post helps,if you get into same scenario….Cheers!

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