Virtual tape libraries: No pain, much gain

Virtual tape libraries make the move to disk-to-disk backup or archiving much simpler, but become familiar with the advantages and disadvantages before making your move.

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What you will learn from this tip: Virtual tape libraries make the move to disk-to-disk backup or archiving much simpler, but become familiar with the advantages and disadvantages before making your move.

A virtual tape library (VTL) is pretty much what it sounds like -- a storage system (disk-based) with its own processor and software that lets it act like a traditional tape library. In an era when disk-to-disk (D2D) has been posited as nirvana, it might seem odd that there would be a demand for tape emulation -- comparable in some ways to putting a command line interface on a modern GUI. But for many organizations, VTL is the formula...

for no pain, with gain.

According to Arun Taneja, chief analyst at the Taneja Group, the demand for VTL is not only strong, it is likely to be very persistent well into the future, despite the fact that "real" D2D products are abundant. Taneja explains that the appeal of VTL has been its simplicity from the user's standpoint.

"Because the disk is made to look like tape there is no need to change any procedures," he says. So, in its favor, Taneja says that VTL has the ability to use all the same scheduling procedures in place for tape -- the backup server simply points to the VTL device instead of the tape device -- and this simplicity spells comfort to many IT people.

"The key thing I have learned over the last 12 months is that VTL, which I always expected would have a brief but strong play in the disk-based backup and restore market, will be part of the environment for years to come," Taneja says.

W. Curtis Preston, an analyst at GlassHouse Technologies, says that regardless of what you call it, the key thing is to get people out of handling tapes, which are especially dependent upon manual intervention by humans to make them effective.

In a recent article in Storage magazine, Preston outlined the two sides of the VTL picture. On the plus side of the ledger, Preston says the benefits including easier management and improved performance, since the VTL handles all the provisioning and does it much faster than a real tape system. VTLs are also shareable among servers, he says.

On the other side of the coin, Preston says that VTLs are not inexpensive, ranging from $4 per gigabyte to more than $12 per gigabyte. However, he says that this is comparable to other D2D backup schemes, which means there's little or no cost penalty for the ease of conversion provided by VTL.

In fact, Taneja says the advantage of going to VTL boils down to four things:

  • Backups become faster
  • Backups become more reliable
  • Restores become faster
  • Restores become more reliable
  • "Those four statements cover a lot of ground because all D2D and indeed all data protection products deliver across those four dimensions," says Taneja. In fact, enhancing those four dimensions is THE characteristic of disk as compared to tape.

    According to Taneja, VTL gets high marks all around for performance and for simplicity. He says he thinks the reason VTL is doing so well compared to other D2D technologies is because the customers are happy with the performance boost they are getting across those four dimensions.

    "IT is so good relative to tape that they are totally satisfied -- our surveys show it at virtually 100%," he says. However, given human nature, Taneja says he wonders whether users will be as satisfied in a few years when they start to think about the higher performance available through other D2D schemes.

    Longer term, Taneja says some companies that adopt VTL probably will be disappointed that it doesn't fully match the performance of a traditional disk storage system. However, he says emerging compression technology, such as HyperFactor, which is used in Diligent Technologies Corp. ProtecTIER to achieve 25 times the storage density of traditional devices, offers the potential to dramatically improve the price-performance of all D2D systems, including VTL.

    "When you get those kinds of efficiencies applied to VTL, it makes me really bullish on the technology," he says.

    For more information:

    Virtual tape evolves to survive


    About the author: Alan Earls is a freelance writer in Franklin, Mass.

    This was first published in October 2005

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