Scale-out approaches avoid the system sizing problem because of the modularity of the architecture. Customers can right-size their purchase to the current environment plus reasonable growth. Then as data grows, more building blocks can be added as needed without concern for a forklift upgrade. This makes the upfront purchase potentially more cost-effective and avoids costly upgrades downstream.
A final argument against the scale-up approach is technology obsolescence. IT professionals are all too familiar with the concept of buying a new product only to find it reaching end of life shortly after purchase. This problem is exacerbated when you make the decision to buy a larger controller that allows for greater expansion runway. The controller causes you to lock in to the then current technology. And as the vendor releases a controller based on newer technology, the only way to leverage it is to go through another forklift upgrade.
Scale-out approaches may avoid this (depending on the vendor) by allowing users to mix and match different generations of building blocks in the same system. Assuming the vendor guarantees the hardware can be upgraded to the latest and greatest software, you can avoid the need to rip and replace expensive components to take advantage of the vendor's newest offerings.
There are a number of vendors that offer scale-up approaches to disk-based backup and a number that offer scale-out. As you decide, weigh the perceived simplicity and familiarity of scale-up with the technical and economic benefits if scale-out approaches.
ExaGrid Systems is the leader in cost-effective scalable disk-based backup solutions with data deduplication.
Read more about data center in Network World's Data Center section.