NetApp's announcement earlier this year that it was backing away from developing advanced deduplication capabilities for its virtual tape library products has touched off a new round of speculation about the future of virtual tape libraries in backup and data protection enviornments.
After deduplication leader Data Domain was lost to EMC Corp. in a bidding war, it was announced that NetApp was discontinuing its NearStore VTL, its own backup data deduplication product.
A VTL is a chunk of storage that is organized to appear as a tape library to the backup server. They gained popularity a few years ago because they could be dropped into a backup architecture with a minimum of changes to the backup server and software. To the server and software, a VTL looked just like a tape library -- a very fast tape library that helped companies stay within increasingly stringent backup windows. The configuration that needed to be done was between the VTL and the actual tape and this was usually straightforward.
Over the past few years, VTLs acquired another major advantage: data deduplication. As VTL vendors added deduplication as an option, tape image sizes shrank by as much as 20 to 1. That made it even easier and less expensive to manage the tape behind the VTL.
All these advantages still apply, but as the market matures, the limits of VTLs have become more apparent as well. Fundamentally VTLs are a stopgap, designed to integrate disk into existing backup and data protection architectures as seamlessly as possible and willing to compromise on things like cost to get relatively painless integration. One result is that VTL products generally cost more than a conventional disk backup array. Further, as disk-based backup products and backup software have matured, emulating a tape library has become has become less necessary. For example, many enterprise backup products now support disks or network-attached storage (NAS) directly.
The future of virtual tape libraries gets mixed reviews
The latest data from market research companies such as Enterprise Strategy Group (ESG) seems to indicate a mixed picture for virtual tape libraries. VTLs aren't going to go away any time soon, but they aren't promising to take over the backup world, either. They can still be a solid option for medium and large enterprises because they offer ease of integration into an existing tape environment. In some cases the savings in integration costs, training, etc. will cover the added cost of the VTL, but there is increasing evidence that VTLs are not for everyone.
Implementing a VTL involves minimum reconfiguration and no new software. Also, if you have a large investment in your present tape-based system, (hence the attraction to medium to large firms), you minimize the cost of adding a tape layer by using a VTL. But it's not a solution for everyone. Small- to medium-sized businesses (SMBs)or companies with a minimal investment in tape probably aren't going to be interested in VTL because straight disk is much cheaper.
According to the Enterprise Strategy Group's 2010 report, "The State Of Virtual Tape Library Technology," interest in VTLs strongly correlates with existing investments in tape and the amount of data being managed on tape. This means that medium and larger companies are more likely to find VTLs attractive.
For companies that don't have a large investment in a tape-based backup architecture, especially smaller enterprises, the benefits of the extra cost of a virtual tape library over conventional backup to disk is less clear. Deduplication is still a huge advantage, but at the same time, non-VTL disk backup systems also offer deduplication (as does most backup software). Ease of integration with existing backup software may or may not favor a VTL depending on the specifics of the backup software. As almost all backup software now supports backup to disk natively, the ability to emulate tape becomes less of a concern.
Finally, the comfort level of the IT staff with the existing system can play a role in the decision to use VTL. If a lot of effort has been invested in setting up procedures based on tape (such as multiple virtual tape drives) it may make sense to use a virtual tape library to continue those things.
The cost of virtual tape libraries
While virtual tape libraries are almost always more expensive than a file system target array, the cost differential may be less than you'd expect. VTL appliances for SMBs typically start at approximately $6,000 (for an entry-level Hewlett-Packard Co. (HP) StorageWorks D2D2500 with 3 TB of disk storage and data deduplication), and can cost more, depending on features and the amount of storage supported.
Fundamentally the question is not "can a VTL do the job?" It almost always can. The real question is the cost of a VTL versus disk-to-disk backup and the ease of use of the two technologies in your specific data storage environment.
About this author: Rick Cook specializes in writing about issues related to storage and storage management.
This was first published in September 2010