Hello Jiff Lemon, Yes you can take your MD1200 from your server and add it to your MD3600i.  What you will want to do is that if you don’t need the data on the MD1200 then what I would do is to remove any virtual disk that are on the MD1200 prior to connecting it to your MD3600i so that it will just see the space from the MD1200 & not any configuration as that can cause an issue when connecting your MD3600i to your MD1200.   So when you connect the MD1200 to your MD3600i you should see the drives from the MD1200 show up as free space that can be assigned to any disk group or virtual disk that you would like.  The new space will not be assigned to any disk group without user interaction. Last is that you will need to power down your MD3600i to connect your MD1200.  You need to power down the MD3600i so that on its reboot it can scan the raid controller and see that there is a new device added & then it can add that to the MD3600i.  You need to also make sure that you power on the MD1200 first & wait about 5 minutes for it to come to a ready state before powering on your MD3600i.   Please let us know if you have any other questions.
I've currently got a couple of MD3600i's at sites; In the same sites I've a couple of Poweredge servers with MD1200 DAS SAS shelves. I'm looking at removing the shelves from the Servers, and adding them to the 3600's.  I'm not expecting any data on the shelves to transfer over, both 3600's have additional physical support feature keys. My only concern is that the MD3600's are 900GB drives, the MD1200's are 2TB drives. My questions are: 1) Is what I'm planning feasible? 2) Would the new drives show up a separate available pool of storage? Again, I'm not going to be trying to spread any current Luns onto the new drives, just create new luns on these drives. 3) Is adding storage a hot swap event? Can I add the shelf via the external SAS or does it require power down?
Expansion of MD3600i (adding disk shelf)