Definitions of an enterprise virtual tape library (VTL) environment vary, but vendors and analysts generally agree that an enterprise-class virtual tape library should back up at least tens of terabytes of data daily and be able to store hundreds of terabytes of data. These high-end virtual tape libraries also need to scale easily and support complex backup and recovery environments, such as those that include multiple remote offices or multiple VTLs in the storage fabric.
The ability to easily add disk capacity is important not only because organizations are backing up more and more data all the time, said 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 virtual tape library environment, said Andrei Shishov, VP of backup platforms engineering at EMC Corp. Reliability is often provided through features such as clustered failover among virtual tape library nodes, as well as redundant components such as power supplies within individual nodes.
Performance is another basic requirement for an enterprise virtual tape library, so it can back up data quickly enough to fit within an organization's backup window and restore files quickly when needed, said Whitehouse. Exact definitions of what is sufficient performance vary, although Peter Eicher, director of product marketing at FalconStor Software Inc., estimated the minimum at 300 MBps to 400 MBps. 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,...
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" support for a variety of backup applications is also a must-have, said Whitehouse. Then there's the need, added Shishov, for the virtual tape library 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 disaster recovery), have made data deduplication a must-have feature for enterprise virtual tape libraries. 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.
Ease of management is key to minimizing the VTL's total cost of ownership, and includes everything from the clarity of the user interface to the ability to easily view and manage groups of VTLs from a single console. Specific features to consider are how easy it is to access all VTLs in a group through a single sign-on, and the ability to view a consolidated report for all the systems and make simultaneous changes in common configuration settings.
Security wasn't a key requirement cited by users or analysts (see How virtual tape libraries compare for a look detailed look at enterprise tape library requirements) because VTLs are generally used in data center environments, which are regarded as secure. Security becomes more important when data leaves the data center stored on tape, so most users said they perform encryption at the tape library and not the VTL. However, some vendors, such as FalconStor and Sepaton Inc., do offer encryption in their VTLs.
Depending on whether a virtual tape library is used along with or as a replacement for tape, users might need it to write directly to or read directly from a physical tape. While most VTLs can import and export tape, said ESG's Whitehouse, another important consideration is whether the backup software's catalog is updated to reflect any changes in the data stored on the virtual tape library so backup administrators can more easily track the location of the backed up data.
How virtual tape libraries compare
Enterprise requirement
Metrics
Enabling technologies
Major vendors
Scalability/Performance
Back up at least tens of terabyte daily; store hundreds of terabytes overall
Clustering; grid technologies; automatic load balancing; independent scaling of VTL; dedupe hardware
EMC Corp., FalconStor Software Inc., Fujitsu Siemens Computers, Hewlett-Packard Co., Sepaton Inc., Sun Microsystems Inc.'s StorageTek Division
Reliability
Continue operating, with minimal impact on performance, after hardware or software failure
Within VTLs, RAID and redundant hardware. Among VTLs, clustering, grid architectures with automatic failover.
Copan Systems Inc., EMC, FalconStor, Fujitsu Siemens Computers
Manageability
Ability to view and manage multiple VTLs as single units; automation of routine tasks
Centralized management consoles; dynamic resizing of VTL cartridges
Data Domain Inc., Diligent Technology Corp. (an IBM company), FalconStor, Overland Storage Inc., Sepaton
Source: Analyst interviews
This article originally appeared in Storage magazine.
About this author: Robert Scheier is a frequent contributor to "Storage" magazine.
