Some early data centers placed a disk on each physical server that all VMs shared. That is, when the provider started a new VM, the provider dedicated part of the physical disk to the VM, and did not start additional VMs after the entire physical disk was allocated. The approach meant that although some physical servers might remain lightly loaded, no more VMs could be started on the servers. The approach also meant that if a tenant overestimated the amount of disk space needed, much of the disk space on a server might be unused. Describe the storage technology a modern data center uses to avoid the storage problems early data centers experienced, and explain why the technology does not leave disk space unused.