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VTLs: What's the big deal?

Nearly every leading storage vendor now has a virtual tape library product, and nearly every customer I talk to is interested in VTL or has already implemented it. Okay, so a VTL system emulates a tape library… but what else does it do? Is this just a feature or is it a separate category of storage that is sustainable?

Enterprise Strategy Group (ESG) has seen a rising interest in virtual tape libraries (VTL) throughout 2004, followed by aggressive planning, budgeting and implementation in 2005, and we believe that it will start to become a requisite part of the backup ecosystem in 2006. ESG Research bears this out, with 76% of customers stating that they would replace some of their tape libraries with disk-based products.

In March 2005, ESG Research published a report that surveyed 163 storage professionals and IT managers at North American private- and public-sector organizations. The following is a summary of our key findings:

  • Tape library challenges are widespread.
  • The limits of tape technology are impacting applications and business processes.
  • Users will replace tape libraries with disk-based alternatives.

VTL products are appliances that emulate any number of well-known tape libraries (e.g., ADIC, IBM, Quantum and Sun STK). Backup applications (e.g., CommVault, Legato and Veritas) recognize the VTL appliance as a tape library, making integration of a VTL an easy and transparent process. The value of VTL is straightforward, making it somewhat of a "no-brainer" for companies. The benefits of VTL include the following:

  • Increased backup performance
  • Improved recovery performance
  • Reduced media management issues

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VTL and disaster recovery
Most VTL products provide remote replication in order to copy backup data between VTL systems over long distances. Using a VTL product can be less expensive and easier to manage than primary storage systems when performing remote replication. Performing remote replication using VTL enables companies to make remote copies of ALL of their data via a single platform. The VTL can be the backup repository for any number of storage systems, including SAN, NAS and even internal or DAS primary storage. Since all of the company's data can be backed up to a single VTL appliance, the backup data can then be replicated to a remote site for disaster recovery (DR) and data protection. This is a much simpler and more cost-effective approach than implementing remote replication on multiple SAN, NAS and DAS storage systems. VTL products can provide a centralized way to protect primary data stored on heterogeneous storage systems.

The one trade-off of this approach is that recovery point objectives (RPO) are typically going to be 24 hours, since backups are usually done once a day (or night). Compare this with synchronous mirroring, with a theoretical RPO of zero, or asynchronous mirroring, with an RPO that ranges from seconds to minutes or hours. However, a large number of companies are still doing nothing more than backing up to tapes, which are then vaulted off-site for DR. Utilizing a VTL system with remote replication that provides an RPO of 24 hours, offers greater protection than most companies using tape backups and off-site vaulting have today. This is especially important, since ESG Research found that 80% of the customers we surveyed were not sure whether all of their backups were reliable and recoverable.

Tape export and tape copy controversy
ESG Research also found that customers are holding onto their tape libraries. Most companies are satisfied with their tape libraries and will continue to use them for long-term archiving. That is why it's important to somehow have your backup data on VTL systems and tape libraries.

There are two popular methods for achieving this: The first is a tape export feature that is a part of the VTL software features. The VTL system will export the backup images to the tape library instead of relying on the backup software to perform another backup. The advantage of doing this is that it saves time, since the backup data doesn't have to be sent by the backup server over the network to the tape library. The disadvantage is that you need the VTL system to recover the data.

The other method is a tape copy feature that is supported by most backup applications. Once you run a backup to the VTL system, you can run the same process over again to the tape library. This process does not require a whole new backup. You simply have to copy the backup already performed to one backup target (the VTL system) to another backup target (the tape library). This is a fairly standard process that will work with any backup target -- VTL and tape library alike. This means that any VTL system will support it. If the VTL system blows up or goes away, the backup software can simply recover the data from tape. The advantage is that it is an independent process that is widely used. The disadvantage is that it requires the resources of the backup server to send the backup jobs to the tape library.

Users quoted in an article in SearchStorage in November took FalconStor to task for not having a good tape integration process. FalconStor does support the tape export function but it's not mandatory that any of its customers use it. Every VTL product works with tape copy including FalconStor and many VTL systems don't have any tape export feature. Diligent, Quantum and Sepaton do not support a tape export feature but rely on the tape copy function. FalconStor should not get penalized for having an optional tape export function when they by default also can work with the backup software's tape copy capability.

I believe that VTL is here to stay. Some believe that it's a feature and not a product. However, VTL systems need to be tuned and tested to work optimally with backup and recovery. VTL systems will support more functionality, including remote replication, data de-duplication and search capability.

About the author: Tony Asaro is the senior analyst for Enterprise Strategy Group.

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