Disk Encroaches on Tape's Backup Territory

In many organizations, tape emerged as a primary backup mechanism for the simple reason that it was much less expensive than disk storage. However, enterprises never liked using tape very much -- it was slow, the media was often unreliable, and maintaining tape libraries was a labor-intensive task.

Consequently, many companies have been on the lookout for a better option. With the steady decline in prices for disk storage, it has become a replacement for tape at some companies. Virtual Tape Libraries (VTLs), which mimic tape backup systems while storing information on disk, deliver the robust features found with a tape backup system while eliminating tape's shortcomings.

As a result, the VTL market has been growing at a rapid rate. International Data Corp. (IDC) found that worldwide revenue increased from $830 million in 2007 to $930 million in 2008. In recognition of that trend, many vendors have moved into the VTL arena. Dell, EMC, FalconStor, HP, IBM, NetApp, Overland Storage, Quantum, Sepaton, Spectra Logic, and Sun are some of the companies in this space.

Corporations and vendors have invested a great deal of time, effort, and money designing efficient tape backup systems. VTLs enable companies to continue to rely on tape backup software but write information to disk rather than to tape.

Falling disk pricing has been the main driver behind the migration to VTLs. In the past, disk cost 20 or more times as much as tape for the same capacity. Recently, technical advances have lowered that gap, so disk commands only three to four times as much as tape. Because it is much simpler to deploy and maintain, disk has become a potential tape replacement for more companies.Moving to a VTL offers companies many advantages, with speed being a main attraction. Writing to disk can produce a 10X (or in some cases even greater) performance improvement.

The time savings let corporations shorten their backup windows. "Because many companies have been expanding their data volumes, they have been having trouble completing their backups within needed timeframes," says Robert Amatruda, research director for tape and removable storage at IDC. Rather than taking multiple hours or forcing companies to backup information only on weekends, VTLs can enable an enterprise to backup information daily.

VTLs can also help with file restorations. Here, a file is restored from disk, which is often acting as a cache in front of tape drives. Recovering information can take minutes (or even just a few clicks of a mouse, depending on the backup system used) rather than the hours or days often seen with tape backup systems.

In addition, disk tends to be less complicated -- and therefore more reliable -- than tape. Tape subsystems include multiple components, which can frequently malfunction or break down. Many companies find that their tape systems routinely do not backup information properly. Moving to a VTL can therefore improve the rate of successful backups.

By dumping their tape systems, companies can improve their data redundancy. Data from virtual tape cartridges can be sent over a wide area network to a secondary location that serves as a disaster recovery site.Yet there are challenges in deploying these disk systems. VTLs have been shipping for a handful of years and are still an emerging technology. Scalability is one issue where they have limitations. Large organizations are now able to deploy vast tape libraries, with 10,000 virtual slots across up to 100,000 virtual cartridges. VTLs often cannot match those numbers.

Data de-duplication is a hot topic in the storage market. While that feature is in place in some VTLs, it has not available in all and its implementation is still a work in progress in many cases.

One goal for VTL vendors is to take advantage of the robust features that suppliers have developed in tape backup systems through the years. Consequently, a company has to make sure that its VTL supports its backup system, such as EMC's Networker, IBM's Tivoli Storage Manager, or Symantec's NetBackup. However, not all VTLs work with all tape backup systems.

The pricing for VTLs can be high. These products usually start near the $50,000 mark and can quickly shoot past the six-figure range. Large enterprises can spend more than $1 million on a VTL. In these tough economic times, many firms may find it difficult to justify such a significant investment.

Because of the high prices, VTLs have not been popular in small and medium businesses. In most cases, these companies have not been using tape systems and see no need to do so now. "Small and medium business market will simply use a disk system for backup rather than go to a tape solution," notes Dave Russell, a research vice president at Gartner.VTLs are having a major impact on the backup market. While they are not a panacea, many companies are finding that they can help improve their backup system performance and are using them to either replace or supplement their tape systems.