Hello mrshahin, The MD3000i is hot pluggable so you can add more drives to it without powering it down.  You can add the drives to either side.  If you are looking to expand your virtual disk then I would suggest that you add them to the side that has the 3 drives.  if you are looking to create a new virtual disk then you can add them to either side & create the new virtual disk.   Please let us know if you have any other questions.  
Hi, We have a Dell power vault MD3000i, I want to add 3 more new drives to it, is the MD3000i hot-pluggable? or first should I power down the device? also currently the first half of the device containes 3 drives should I first full the first part with drives or I can add the new drive into the second half which is  elso empty?   Thanks
hot-pluggable or not