Hello,
As Subhajit has stated - either adding drives to the D2700 or the controller enclosure should not be an issue. The only caution I would make is adding drives to a linear vdisk using expansion. This process takes a long time and while expansion is running you cannot do a rebuild. If you are going to expand a linear vdisk, I would recommend a backup first. Or to perform a backup, delete the vdisk, and recreate a new vdisk with the correct number of drives and restore from backup.
As you add disk-groups and vdisks, my recommendation is to balance across the controllers so you are using both controllers and all available host ports evenly. This will maximize your CPU usage on the controllers and provide you the best performance possible.
Cheers,
Shawn