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Virtual tape libraries in depth

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State of the VTL industry

VTLs came about to address specific backup issues. Let's look at how they've progressed in those areas they were supposed to fix.

Scalability. Scalability isn't just an issue for big enterprises; it's also necessary to meet the needs of small- and medium-sized businesses (SMBs). When the VTL market was in its early days, there were very few products that could scale well for either of these segments. But times have changed, and there are now several products that scale both up and down. With some notable exceptions -- Copan Systems Inc., IBM Corp., NEC Corp. of America and Sepaton Inc. -- all VTL/IDT vendors offer products for SMBs. Companies with less than 20 TB of data to back up each night can choose from a number of products -- some less than $5,000 -- that offer a lot of the same functionality available in high-end products. Offering products to the SMB market before they're deemed bulletproof typically spells failure, so the arrival of these SMB virtual tape libraries and intelligent disk targets is a sign that vendors have done a good job of working out any kinks in their products.

Midsized enterprises with 20 TB to 40 TB to back up each night can choose from almost every vendor. To back up that kind of data you need a system capable of handling 500 MBps to 1,000 MBps. Almost every vendor listed in the "Product sampler: VTLs and IDTs" (below) sidebar has a product with that capability.

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The high end of the enterprise (companies with 40 TB or more to back up every night) has fewer products to choose from. Users with that much data to back up connect large servers to a Fibre Channel storage-area network (FC SAN) and back them up using local-area network (LAN)-free backups. The last thing those users want to do is send those backups over IP; therefore, a product targeting this market segment must have FC as a transport.

Another reason why there are only a few products appropriate for this market is the lack of global data deduplication in some products. A user with 100 TB to back up each night needs 2,300 MBps throughput. They won't want to (nor should they have to) create and maintain three separate 33 TB backup collections that'll back up to three devices that can only handle 40 TB per night each. They need a single system that can handle this load over FC without splitting it into multiple backup collections. There are only a few companies with products capable of doing that: FalconStor Software Inc. and Sepaton (and their respective OEM partners Copan Systems and Sun Microsystems Inc., and Hewlett-Packard [HP] Co.). The aggregate throughput of NEC's Hydrastor is actually much higher than 2,300 MBps, but it doesn't yet offer Fibre Channel as a transport. If you need this kind of throughput over FC, but don't need deduplication, EMC, Fujitsu and Gresham Storage Solutions Inc. have products that can help.

Noticeably absent from the list is EMC/Data Domain. Their fastest FC-based VTL runs at 900 MBps. Data Domain's DDX "array" boasts a number much higher than that, but it's actually 16 separate DDR units in the same rack that aren't integrated as far as deduplication goes. Data Domain doesn't support global deduplication, although the company has said it's on its roadmap. However, there's been no indication as to when this feature may become available.

Ease of use. VTL and IDT products range from the "ridiculously easy" to use to "so hard you can't believe it passed any kind of functionality testing." But most are relatively easy to use. Still, ease of use varies considerably, so you should definitely test with any products you're considering.

Integration with backup appliances. All VTLs and IDTs can be backup targets for just about any backup software product on the planet, and most can also replicate their data to another VTL/IDT. But few products today integrate with the backup software so that it knows about replicated copies and can use them for restores and copies to tape.

This was first published in December 2009

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