We can see the issue that is caused when we have deleted virtual disks inside a disk group by clicking on the "Disk Groups & Virtual Disks" link under the Summary tab on the Dell Storage Manager application.

As shown above, you will see areas of "Free Capacity" which are stranded from each other, as they are not contiguous.

To perform the disk group defragment, you will need to have installed the Dell MD Storage Manager CLI/Utilities onto a host (usually the same host that has the Dell Storage Manager installed will have the Storage Manager CLI installed as well).
You will use the "SMcli" utility to issue commands to the Dell MD3000i storage array, which is located under the following path depending on your operating system type:
C:Program Files (x86)DellMD Storage Managerclient = 64bit Operating System
C:Program FilesDellMD Storage Managerclient = 32bit Operating System

Type the following command in order to start the disk group defragment:
smcli -n hostname -p password -c "start diskgroup [1] defragment;"
The "hostname" field above should be replaced with the actual hostname of the storage array.
The "password" field above should be replaced with the configuration password for the array.
The diskGroup # is actually the identifier of the disk group. Ours happens to be the number "1".

Next you should receive a screen like the above which shows the command completing successfully.

You can verify that the disk group defragment worked by looking at the Disk Groups and Virtual Disks summary again. It should now no longer show multiple "Free Capacity" entries! (1)
Notice the icon has changed for the virtual disk (2) which shows it is defragmenting the data.

To monitor the process of the defrag, you have to look at a virtual disk that is being defragmented. Use the following command:
SMcli -n hostname -p mypassword -c "show virtualDisk [vdiskname] actionProgress;"
The "hostname" field above should be replaced with the actual hostname of the storage array.
The "password" field above should be replaced with the configuration password for the array.
The "vdiskname" field above should be replaced with the virtual disk name.

Once the command executes, you should see the Defragment operation running as well as the percentage complete. Defragmenting the virtual disk will usually take awhile, so be patient during this process.

In order to speed up the defragment operation or any other RAID rebuild process, you can run the following command:
smcli -n hostname -p mypassword -c "set virtualDisk [virtualDiskName] modificationPriority=highest;"
The "hostname" field above should be replaced with the actual hostname of the storage array.
The "password" field above should be replaced with the configuration password for the array.
The "vdiskname" field above should be replaced with the virtual disk name.

Once the command executes, you should see a screen like the above.

You can confirm the rebuild priority was changed by using the command listed above for monitoring the virtual disk. This will also show the rebuild priority, as circled in our screenshot above.