Today's storage mechanisms are all about squeezing as much data into as little space as possible. Virtual tape library (VTL) software contributes to the space-saving cause by using hard-disk storage systems to emulate robotic tape libraries for the purpose of cutting down on using up precious storage real estate.

In this Clear Choice Test we set out to evaluate VTL systems that incorporate data deduplication (see primer) to further reduce the overall storage footprint while maintaining a high level of data maneuverability and overall system manageability.

We invited all vendors who ship VTL software to participate, including Quantum, Avamar (now EMC), Copan, Data Domain, Diligent, FalconStor, Network Appliance and Sepaton. Quantum, with its DXi5500, and Data Domain, with its DD560, were willing and able to participate within our testing window. FalconStor's new product is in our lab now. We'll post those results online as soon as they are available.

We used Symantec's BackupExec 11d running on a Windows 2003 server to back up 2TB of data from a 2Gbps Fibre Channel storage system to each device. We backed up the same data a second time, and ran a script that changed 1,361 files totaling just over 60GB worth of changes and ran a third backup process (see How we tested VTLs).

Both appliances got equally high points for providing efficient compression and high data-throughput rates. While their performance indicates they should be able to support multiple simultaneous backup streams, we must caution that your mileage likely will vary depending on the type of data, its inherent compressibility and its susceptibility to deduplication.

Product DD560 DXi5500 Vendor Data Domain Quantum Price as tested $105,000 $139,000 Pros Can support multiple hosts via a single Fibre Channel port; easily expands to multiple controllers and drive shelves. Easy GUI configuration; emulates more actual libraries; price includes four Fibre Channel ports. Cons Configuration must all be done via command line.   Score 4.5 4.5 The breakdown  Data Domain   Quantum  Installation 25% 4 5 Performance 25% 5 5 Management 25% 4 4 Scalability 25% 5 4 TOTAL SCORE 4.5 4.5 Scoring Key: 5: Exceptional; 4: Very good; 3: Average; 2: Below average; 1: Subpar or not available

Click to see: Compare Data Domain and Quantum VTLs