Building on the description of cloud storage facilities in Chapter 4, this chapter completes the description of virtualization technologies by examining the virtual storage facilities used in data centers. The chapter begins by describing the two types of persistent storage: disks and files. it explains the block-oriented interface used with disks and the byte-oriented interface used with files. The chapter then examines the concept of remote storage, and explains that both remote disk and remote file systems were invented decades before cloud data centers. The chapter covers Storage Area Networks (SANs) and Network Attached Storage (NAS) systems used in cloud data centers. It shows how SAN systems map virtual disks onto physical disks. It also explains that early SAN systems used special-purpose networks, and describes a Hyper-Converged Infrastructure (HCI) that sends SAN traffic over a conventional data center network. Finally, the chapter describes object storage technology, such as the AWS S3 object store.