Disk-based backup solutions are gaining momentum, but VTLs may keep tape in the game Disk-based backup is becoming increasingly popular, thanks to the ever-growing, gigantic amounts of company data that needs protection combined with inexpensive, large-capacity disk arrays.An array of disk drives is faster, less expensive, and takes less space than an equal number of tape drives; therefore, a CTO can add capacity and performance to backups for less money while making more efficient use of the floor space.Performance of disk backups is not only faster, it’s more predictable. Tape backup speed degrades to a crawl when the server cannot maintain a steady transfer rate. When that happens, a tape drive loses momentum and begins frequent rewinding and repositioning of the medium under the read-write heads, waiting for the dataflow to resume. Disk-based backups are, of course, unaffected. In addition, although the primary target of disk backup is online storage, data needing long-term retention or archival can be easily copied or moved offline to a physical cartridge, summing up the benefits of disk and tape media.A couple more strikes for disk-based backups: Achieving high availability for a disk array is less expensive and challenging than reaching the same goal for tapes. Moreover, backups to tape are often disrupted by trivialities such as the wrong barcode on a cartridge or media errors.Tapes still have their irreplaceable role, but the proliferation of disk-based backups can have a significant drag on the revenues of tape vendors and therefore on the amount of dollars available for R&D. If this sounds somewhat threatening for manufacturers of tape libraries, well, it is.Interestingly, their reaction to that threat has been to join the enemy, so to speak, by developing VTLs (virtual tape libraries), disk-based backup appliances that mimic and work in synergy with their tape libraries.Once found mainly on mainframes, VTLs could quickly become a popular tool for client-server customers because they combine the benefits of disk-based backups with seamless transparency to backup applications and offer policies to automate copying or moving data to physical tape media. Some recent examples of VTLs from tape vendors are the ADIC PathLight VX and Quantum DX100 and DX30, but other vendors also have or are developing similar solutions.For example, StorageTek plans to offer a “disk buffer” with its upcoming super-library, the StreamLine L8500, to isolate backup jobs from slow performance and media errors typical of tapes.For companies such as Alacritus Software, FalconStor, Troika Networks, and Ultera Systems that have been offering their virtualized tape solutions for some time, the recent opening to VTL from major tape vendors brings probably more competition but also a nod of acknowledgment. The future looks promising for VTLs: Although other data protection technologies will probably shrink that number, companies will continue to run countless backup jobs every day into the near future.