Volume Controller includes a dynamic data-migration function that helps administrators migrate storage from one device to another, without taking it offline. This helps administrators to reallocate and scale storage capacity without disrupting applications. The San Volume Controller makes possible virtual tape and replication and also the chance to use cheap storage as the backup for expensive but highly reliable storage like the ESS. Another form of virtualization is to make a device appear to be something quite different. As an example, a particular system which sells in relatively small numbers might only support a limited number of peripheral devices. It might, perhaps, have only one particular type of tape drive that is supported and the price per megabyte of storage media can be very high. Due to the economies of scale, media for a different form of tape storage, commonly used on a platform that sells in much higher numbers than the former can be much cheaper. In this case, if there is a need to back up very large amounts of data, there is a high incentive to make the first platform be able to communicate with the second form of tape device. Sometimes a device driver can be written for the operating system to make the device work. It is often more practical to use the approach of virtualization. That is, to make the tape drive look like the kind of tape drive that the first platform supports. Another type of virtualization is at the file system level. The IBM TotalStorage SAN File System, based on IBM Storage TankTM technology, is a network-based heterogeneous file system for data sharing and centralized policy-based storage management in an open environment. The SAN File System enables host systems to plug-in to a common SAN-wide file structure. Files and file systems are no longer managed by individual computers, but managed as a centralized IT resource with a single point of administrative control. Data sharing and collaboration is enhanced through a single global name space across heterogeneous server platforms, with high performance and full locking support. The San File System reduces storage needs by pooling available and temporary file space across heterogeneous servers and storage platforms and reduces the need to maintain duplicate data for sharing. The San File System can simplify and lower the cost of data backups by offering application server free backup and leveraging built in file-based FlashCopy Functions. 3.22 Solutions The main support for Fibre Channel development came from the workstation market. While in the mainframe platform the I/O channels have evolved allowing storage attachment and sharing through multiple high speed channels, and fiber optic cabling was introduced with ESCON, workstations have been using SCSI as the common interface for storage attachment. Chapter 3. SAN features 177