Why is everyone jumping on the clustered storage bandwagon? In my opinion, it is granularity that provides a "pay as you go" scaling of performance and capacity. With a dual controller architecture, the storage manufacturer needs to build enough processing power in the controllers to power the performance and capacity expectations of a fully loaded system. With a cluster storage system, not only can you add either I/O performance or capacity independently from each other, but you can do so as you need it. Also unlike many dual controller systems that essentially hit a wall on performance, forcing an upgrade to the next controller platform, clustered storage is basically self-upgrading. By adding new nodes to the cluster you are essentially adding more performance or capacity and extending its reach. The clustered architecture should be able to handle mixed nodes and as a result will self-upgrade to newer, more power-efficient components, over time.
Most cluster storage solutions today are NAS based, focusing on file services. They make ideal targets for cloud computing and archiving. Clustered storage is moving into prime time and companies such as Isilon and OnStor make a clustered storage solution for primary NAS storage. So how does this threaten the dual controller architecture? The next frontier is in block storage, companies like 3PAR and IBM's XIV are offering block-based clustered storage, bringing this self-upgrading granular application of performance and capacity to databases and other block-based needs.
There won't be a dual controller vs. clustered architecture battle like there was with SAN vs. NAS or iSCSI vs. Fibre Channel. There is little anti-cluster sentiment out there. It seems to be more a matter of when, not if. Dual controller still has a place today. It has the appearance of being simpler on installation (no cluster to get working, which can sometimes be an issue) and if you know that your performance and capacity limits are going to be well-handled by a dual controller system, it may also be less expensive.
As always, determine what is important to you and make your choice from there.
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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.