Modular storage systems ushered in a new era in storage by delivering more flexibility and modularity than their monolithic storage systems predecessors. A new generation of storage system, the Networked Storage System, is now creating a dislocation in the marketplace by taking a page from distributed computing models and leveraging advances in storage networking.
Users with tight IT budgets have readily adopted modular storage systems as a path to acquire storage infrastructure at a fraction of the cost of large monolithic systems. As growth outpaced the extensibility (up until Fall 2003 most modular storage systems had a maximum raw storage capacity of 35TB) of these modular systems, users were forced to upgrade to a more powerful models or added additional systems. Upgrades required system downtime and resulted in business disruption. Increasing the number of systems meant an upgrade in SAN infrastructure and layers of software applications to manage theses systems. The complexity of managing multiple systems, inefficiencies in the utilization of this storage, and support costs quickly out-stripped the initial savings.
At the core of the issue is the architecture of a typical modular storage system. Most modular storage systems use single or dual storage managers housed in a common enclosure with some number of disk drives. Capacity is increased by daisy chaining additional disk cabinets. A fixed number of disk channels is an architectural limitation for capacity expansion. Host connectivity is limited by a fixed number of dedicated host channels. Performance is limited by the power of the pair of storage managers. Lastly, availability is disadvantaged by a dependency on a common backplane between the storage managers. Challenged to scale modular systems beyond the architectural limitations, vendors added virtualization software, storage resource management software, and a web of fabric switches.
Problem solved.
Not quite. Whatever happened to the simple elegance of modular storage and reducing cost?
The extensibility of modular mid-range storage systems is indeed limited by architecture; however, marketing also plays a role. The extensibility of modular systems is limited in part to protect the premiums associated with high-end systems, and the profits derived from the software and services required to create networks of modular systems.
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