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The ability to easily add disk capacity is important not only because organizations are backing up more and more data all the time, says Lauren Whitehouse, an analyst at Milford, MA-based Enterprise Strategy Group (ESG), but because companies often buy their first VTL to meet the needs of a specific department and then add to it as they see the value it provides.
Because of the number of production servers involved, failed backups are considered unacceptable in an enterprise VTL environment, says Andrei Shishov, VP of backup platforms engineering at EMC Corp. Reliability is often provided through features such as clustered failover among VTL nodes, as well as redundant components such as power supplies within individual nodes.
Performance is another basic requirement for an enterprise VTL, so it can back up data quickly enough to fit within an organization's backup window and restore files quickly when needed, says Whitehouse. Exact definitions
| of what is sufficient performance vary, although Peter Eicher, director of product marketing at FalconStor Software Inc., estimates the minimum at 300MB/sec to 400MB/sec. In addition to improving reliability, clustering can boost performance by spreading the work of reading and writing data, and/or deduplicating it, among multiple VTL servers.
Because enterprise customers "potentially have not only the local data center, but maybe some remote offices to be concerned about," support for a variety of backup applications is also a must-have, says Whitehouse. Then there's the need, adds Shishov, for the VTL software to work with the widest possible variety of backup software, servers and server components, such as host bus adapters and disk drives.
The desire to cut the purchase and energy costs of disk drives, and to reduce the bandwidth required to replicate data among various sites (such as for DR), have made deduplication a must-have feature for enterprise VTLs (see "Dedupe options," below). Some vendors are also introducing massive array of idle disks (MAID) or spin-down features that power up disks only when they read or write data.
This was first published in August 2008