First let me clarify what I mean by data-reduction technology -- also known as COS (capacity-optimised storage) or, when applied to data transfers across a WAN link, COT (capacity-optimised transport).

In essence, COS consolidates fragments having the same content, making it possible to shrink the space needed to store a file to a bare minimum. The size of the fragments and the algorithms used for the optimisation vary, but the common process for all COS solutions is to divide data into similar-size chunks and look for repetitive patterns.

Imagine applying this technique to data backups, which is what Avamar and Data Domain do intuitively. Using COS creates backup files somewhat smaller than the original because of the space saved by eliminating equal chunks. That saved space can be significant; but there's more, as COS has another rule: Identical chunks are backed up only once. Therefore, backup cycles following the first one will have to copy only a small fraction of the original content, because most files change very little of their content over time.

Just think of how many similar patterns you may have in your datacenter (such as OS files from multiple servers), and it quickly becomes clear that COS-empowered backup applications can achieve tremendous compression rates - of 10:1 or larger.

The compression rate translates into leaner, faster backup cycles, but COS also benefits data exchanges between remote offices, with faster transfers and significant telecom cost savings. Not surprisingly, both vendors offer a replication application to complement their main products.

Perhaps the most important effect of COS' unprecedented compression ratio is to make disk-based backups cost competitive with tapes, essentially shrinking the cost/capacity ratio differences between these two media to nearly nothing.

The two vendors developed their COS products using a slightly different approach. Data Domain proposes appliances as target devices for backups, whereas Avamar offers its Axion application stand-alone or bundled with an appliance. Perhaps the most significant difference between the two is that Data Domain integrates with major backup applications, whereas Axion replaces them.

"The DD460 is a disk full system packaged as an NAS target for backup software," says Frank Slootman, president and CEO of Data Domain. "Inside that box is our secret sauce that gives different ways to find redundant patterns and store them uniquely."

As for Avamar, "you can buy our hardware or we give you a bill of material saying 'that's what we tested for good performance,'" explains Ed Walsh, CEO of Avamar. "But in general, [Axion] works on any Red Hat Linux box."

Avamar's new Version 3.5 of Axion has some interesting new features, such as a central management console for multiple systems and expanded support for databases, OSes, and Exchange servers. Axion 3.5 also encrypts data, but the new feature I find most interesting is the file system view that makes all the files in the Axion pool of backups easily accessible to just about any application.

According to Avamar, file system view should facilitate integrating Axion with customers' existing environments, simplifying activities such as copying a backup to tape using conventional backup applications, or restoring files using standard copy tools.

Avamar also anticipates that customers will be able to build powerful queries of their Axion backups by using a search engine, a feat that wasn't possible without file system view and isn't practical with tape backups.

As for Data Domain, its latest announcement introduces a VTL (virtual tape library) option for the DD400 line that makes it possible to emulate up to 47 LTO tape drives and 100,000 virtual cartridges, and connects to an existing storage network via FC (Fibre Channel).

A VTL option for a disk-based backup appliance like the DD400 may seem counterintuitive at first, but it opens the option of storing compressed backups on storage arrays from other vendors, such as an EMC Clariion.

With data growth at many companies doubling every year, deploying a COS system can be the most effective way to maintain sanity and keep data protection manageable. If your backup cycles are getting out of control, consider putting your data on a COS diet.