By Dave Simpson
Disk array vendor XIOtech recently introduced what analysts say is a unique architecture that essentially decouples controllers and disk arrays on a Fibre Channel storage network. The company hopes to differentiate its distributed controller technology, dubbed Magnitude 3D, from traditional monolithic and modular disk arrays (including the original Magnitude) in which controllers and drives are in the same enclosure. The company refers to the architecture as a dimensional storage cluster.
In addition to purported scalability advantages, XIOtech officials claim that the architecture provides better "resiliency" (reliability) versus architectures that have single points of failure (a drawback to the original Magnitude array).
In the 3D architecture, storage controllers (called Dimensional Cluster Nodes, or DCNs) and disk arrays plug directly into a Fibre Channel network. Intelligence is distributed across controllers, and fail-over is provided at the port-to-port (intra-controller) or controller-to-controller (clustering) levels.
Each controller includes three Intel i960 processors and up to eight Fibre Channel adapters (four on the storage side and four on the server side for connection to a storage area network). The disk arrays include Fibre Channel disk drives (from Seagate, which previously owned XIOtech) and are seen by the controllers as a virtual storage pool.
Rob Peglar, chief architect at XIOtech, claims that the two key differentiators are intra-controller fail-over and N-way cluster fail-over. Up to 16 controllers can be clustered. He also claims that the architecture's incremental scalability could be a differentiator. Users can add drives or controllers as needed, as opposed to having to buy frames. "You can buy capacity or performance when and where you need it," says Peglar. "There's no over-buying or over-provisioning."
The architecture is similar to server clustering. "Controllers talk to each other to ensure availability," explains Steve Kenniston, an analyst with the Enterprise Storage Group. "When a controller fails, another one takes over. They've moved high-availability intelligence from hosts to controllers." The architecture does not require host-based software for functions such as virtual storage pooling and replication.
Kenniston also points out that XIOtech has a relatively scalable file system and volume management technology that allows users to add capacity to existing volumes without taking the system down, eliminating planned downtime.