You can however take an unused disk (not part of any raid groups) and add it to an existing raid group.
After it's been made part of the raid group you will have extra space in the raid group (this can take several hours). Now you can create a new LUN in the raid group (don't assign it to any storage groups), right click the existing LUN and select to expand it. Pick the concatenation option and pick the newly created LUN. Your existing LUN now becomes a MetaLUN that consists of 2 components; the original LUN and the added LUN. If you now rescan the disks on the server that's using it you can see the disk has grown. At this point you need to resize the partition to use the extra space that just became available.
You didn't mention the OS on the server that's using LUN 30, but if it's (non-clustered) Windows, you can use this Microsoft article to resize the partition.