During a virtualization project, you find that there are several questions not easy to answer:

Q1. How many users already migrated to the new system and what is the activity on their old hard disk?

Q2. How much storage designated for the project is already in use?

Q3. When the project is completed, how much of the storage is really being used by the users, and what is the purchased storage overhead that is >not in use?

Q4. Should your virtual disk be maintained? (i.e. Defrag)

Failing to answer, puts a big question mark on the success of the whole project:

A1. Don't relay on your records. You know how much storage is installed on every server and workstation, but you don't know how it is being used. This is the time to give more storage to users who really need it, and the only way to look at it is through the data "heart beat"  that reflects real usage of the disk storage.

A2. The only way to make sure how the virtualization project progresses, is to look from the users' point of view. When you have the answer (using the method proposed here), compare it with the formal information you get from the project management.

A3. When you have started the virtualization project, you have defined the disk space needed by the users and servers. Adding the replication factor overhead you have received the total amount of storage that was finally purchased. Now is the time to check the actual storage the users received, and compare it to the amount of storage you have installed. This is the only way to confirm your planning.

A4. If you stop maintaining your virtual disks (Defrag) you will soon encounter performance problems. When you ask the storage expert what is wrong, he will tell you that more storage is needed. (Sounds familiar?). When you finally purchase several more petabytes of storage, the internal rebalancing mechanism will start copying the logical disks into the new storage. This is the best defragmentation technology that was in use many years ago. It would be less expensive to defrag your virtual volumes before you start getting  performance problems - As you still remember from your past experience with real disks.