Virtual tape libraries (VTLs) are increasingly viewed as something akin to a modern day miracle for backup pains. Though VTLs are easy to implement, expedite backups and restores and free up time previously spent troubleshooting failed backups, users also need to recognize what new challenges VTLs introduce.
An initial concern is data portability. VTLs put the data on disk, not tape. Though this approach works well when recovering data locally, it becomes problematic in disaster recovery scenarios when the recovery needs to occur at another site. Organizations must then either copy the data to a removable media like tape or replicate the data to a remote VTL.
Both of these approaches create their own set of problems. If making copies to tape, what or who manages copying the data to tape? This is a task that the backup software can assume but only enterprise backup software packages offer this functionality and creating tape copies manually becomes a new pain point. Alternatively, purchasing another VTL and installing it at a remote site requires the installation of a high speed data communication link between the two sites that has sufficient bandwidth to keep the data between the two VTLs in sync.
This leads to the final problem with VTLs - infinite capacity. With real tape libraries you eject the full tapes and insert empty ones. With most VTLs, users generally do not have this option. Once they are full, they're full. That means users either need to start deleting backed up data or open up their pocket book to buy another VTL.
VTLs are a much needed product in a space fraught with problems. However, VTLs have their own pain points and users should not assume that just because VTLs solve their immediate backup problems that all of their backup ailments are cured.
Jerome Wendt currently works as a storage engineer and storage analyst. He contributes regularly to a variety of industry trade publications and can be reached at firstname.lastname@example.org.