Another post for me that is simple and hopefully serves as an example for people trying to get blogging as #SQLNewBloggers.
The DAC is a really important tool for anyone managing a SQL Server. You might not use it often, but when you need it, you really need it. I’d suggest you connect to your instances one a month or so using the DAC, just to be sure you know how to do it.
The most common reason to use the DAC is when a runaway query is consuming so many resources the user can’t connect. The DAC is guaranteed resources, so you can always connect.
When you use SQLCMD, the -A switch lets the connection method know you want to use the DAC. The DAC only allows one connection, so only one admin can connect. This also means it’s important to disconnect quickly if you don’t need the DAC.
To connect, I use a normal set of parameters, -S for my server and -E for Windows auth. However I then add the -A, which connects me through the DAC.
Once I connect, I can run any of the normal commands, I need, like rebuilding master or killing a connection.
Keep this as a tool in your toolbox and practice regularly.
The first link I saw was from my friend, Pinal Dave.