Tier 4 once was the simplest of all tiers -- it was just tape. The advent of disk-to-disk backup, which has helped most backup strategies, actually has made the tier itself more complex. I also can take a stand that, in some ways, the introduction of disk has made the process of backup itself more complex.When the only target of Tier 4 was tape, the focus was on delivering the data to that tape drive as fast as possible. Tape drives themselves have been plenty fast enough for years now, they're just not very forgiving if you can't deliver data to them fast enough. They slow down and have to reposition, commonly called shoe-shining. Enter disk-to-disk backup. Disk is more forgiving. If you send data to disk slower than what it can receive, there's not the spin down and reposition penalty that there is with tape. Disk-to-disk backup was not only a performance aid, but it also improved the reliability of the data being stored. However, I believe that most tape-related failures are the direct result of shoe-shining.

Disk-to-disk backup had issues. First, even with the new pricing of ATA disk, it was expensive to store terabytes of backup data long term. Data deduplication, the process of identifying and eliminating the redundant data, solved many of the cost issues by delivering a typical 20X storage efficiency. Storing 20 TB's of backups in 2 TB's of space really drove down disk backup storage costs. Deduplication also solved another big issue with disk backups; portability. The challenge with disk backup is that it doesn't have the portability of tape. Because deduplication eliminates redundant data, it only has to transfer new or modified blocks of information. This made replication of entire backups possible. The result has made data deduplication one of the hottest technologies in the market. While not the very first in, early mover Data Domain legitimatized the market and now almost every manufacturer is trying to respond.

Unless you're going to totally replace tape, one of the biggest challenges with disk-to-disk backup is the final integration to tape. Getting data to tape from a disk backup device is very difficult. Many of the current VTL solutions are difficult to implement and maintain. Users also have found that using the current backup software to manage the process is difficult and problematic. Backup virtualization, from companies like Gresham Storage, promise to solve this last problem by managing a back-end movement to tape.

There it is, the Trail of Tiers. By the time we got through this whole trail, something likely already has changed. There are so many nuances to these different tiers and more come to market every day. Stay tuned to this blog and we will keep you posted...

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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.