According to the Enterprise Strategy Group, several new technologies have emerged that can be used as replacements for tape backup.They include:

• Virtual tape library: Software- or appliance-based technology designed to make a disk array emulate a tape library. This provides back-up and recovery performance benefits compared with tape-based solutions but lets users continue using technologies and processes designed to work with their tape environments. Vendors include ADIC, Alacritus, Diligent, FalconStor, Neartek, Overland, Quantum, Sepaton and SpectraLogic.

• Near-line disk target: A disk array that acts as a target or cache for tape backup. These arrays typically offer faster back-up and recovery times when compared with tape and are cost-effective because they're increasingly based on low-cost Advanced Technology Attachment disk drives. Unlike virtual tape libraries, however, they typically require configuration and process changes to existing back-up/recovery operations. Vendors include Engenio, Network Appliance and Nexsan.

• Content-addressable storage (CAS): A disk-based storage system that uses the content of the data as a locator for the information, eliminating dependence on file system locators or volume/block/device descriptors to identify and locate specific data. CAS is often used as a new storage paradigm for archiving reference information. EMC's Centera is an example of CAS.

• Massive array of idle disks (MAID): A disk system in which disks spin only when necessary (such as during read/write operations), reducing total power consumption and enabling massive high-capacity disk systems with comparable economics to tape libraries. Copan Systems' Revolution 200T is an example of MAID.

• Snapshots and incremental capture: A snapshot is a copy of a volume that is essentially empty but has pointers to existing files. When one of the files changes, the snap volume creates a copy of the original file just before the new file is written to disk on the original volume. As such, IT administrators have a second copy of data saved to disk that they can use for instantaneous recovery or as an offline copy for backups. A variety of vendors offer some type of snapshot capability.

• Incremental capture: Vendors in this category can replace existing back-up technologies or co-exist with them. Incremental capture solutions can take snapshots at the block, file or volume level. This gives users more detail when capturing data and offers unique integration capabilities with applications because these products typically write at the block level. FilesX is an example of incremental capture.

• Continuous capture: Includes software or appliances designed to capture every write made to primary storage and make a time-stamped copy on a secondary device. The main objective is re-creating a data set as it existed at any point in time, with the goal of being able to rapidly restore applications. Vendors include Alacritus, Mendocino Software, Revivio and StorageTek.

• Array-based replication: These products have traditionally come from large disk array vendors such as EMC, Hitachi Data Systems and IBM. Early products were robust but expensive and only worked between homogeneous arrays from the same vendor. Today, that requirement no longer exists, prices have come down, and new vendors are getting into the game. Vendors such as EqualLogic, Exagrid and Intransa provide replication with their disk arrays at relatively low prices.

• Host-based replication: Host-based replication software runs on servers. As writes are made to one array, they are also written to a second array. Vendors in this category have made this technology easier to deploy and manage. They include EMC-Legato, DataCore Software, NSI, Softek, Sun, Topio and Veritas Software.

• Fabric-based replication: Enterprise Strategy Group expects a strong trend toward fabric-based intelligence over the next few years because of a number of potential advantages. For example, the sooner an I/O is captured, the sooner it can be sent to a secondary device, thus enabling better performance. Vendors include Brocade Communications, Candera, Cisco, CNT, FalconStor, IBM, Kashya, Maranti Networks, McData and Troika. A variety of traditional switch vendors are putting intelligent blades into their core products, and third-party developers are porting their applications to the blades.