By Jim Damoulakis, ComputerWorld.com,
As backup hardware and software vendors continue to enhance their products, the choice of methods for incorporating disk-based functionality into backup continues to grow. Essentially, this is goodness overall because it means that a wider range of requirements can be accommodated, but it can also cause confusion as well as presenting a risk of selecting the wrong approach when design requirements and technology subtleties are not adequately understood.
From a software perspective, until fairly recently most enterprise backup products were optimized to support a tape backup paradigm. Over the years, these products were enhanced to provide reasonably efficient management of tape devices and media. While disk was also supported as a backup target, by and large it was a secondary consideration. More recently, the situation has shifted dramatically: backup software products are now outdoing each other with each release adding disk-specific features ranging from improved performance algorithms and added flexibility to span disk volumes and file systems to software-based deduplication at both the client and server levels.
In the hardware realm, deduplication is arguably the feature garnering the greatest focus. While designs that utilize disk as cache prior to migration to tape can be accommodated with standard disk storage, using disk as a longer term data store for any sizeable amount of data becomes quite costly without employing a technology like deduplication to greatly reduce capacity requirements. Today, this means one of two options: either a deduplication-enabled NAS device (e.g. Data Domain, NetApp, Exagrid, NEC's Hydra) or one of the handful of virtual tape libraries (VTL) that support deduplication (e.g. Diligent, Data Domain, Falconstor, Sepaton).
The question of whether to opt for NAS or VTL depends on a number of factors, including:
Whether the existing backup application is predominantly tape-oriented or is it a disk paradigm that is well supported? If tape-oriented, VTL may be the best fit.
Similarly, if the backup environment leverages SAN drive sharing (a.k.a. LAN-free backup) today, then a VTL would be the obvious choice.
Is disk intended to primarily be a supplement to tape or a replacement? If there is no need to maintain a tape paradigm, then NAS-based backup may be an option
Cost, as always, is a factor, and there is typically a premium for VTL capability above and beyond the underlying storage.
Of course, individual products also vary significantly in terms of performance, scalability, and method of deduplication, and these factors will certainly play a large role in making a selection.
Expect more developments as other vendors introduce their deduplication offerings later this year. There are already signs of interesting developments, such as the introduction of a hardware-based deduplication interface card from the compression vendor Hifn. All portend exciting new design options for backup architects.
Jim Damoulakis is chief technology officer of GlassHouse Technologies Inc. , a leading provider of independent storage services. He can be reached at jimd@glasshouse.com.
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