Last week, LSI announced their release of “the industry’s first 6Gb/s SAS switch”. The switch offers unique opportunities for cluster managers to improve the architecture of their storage systems.
The value of the SAS switch is its function of transforming a cluster from a NAS (network-attached storage) structure into a DAS (direct-attached storage) structure. With DAS, storage data does not have to be transferred from the SAS protocol to the network protocol (Ethernet or InfiniBand) and back to SAS. The bottleneck of the middle step is eliminated – the LSI switch allows all I/O of data to happen through just the SAS protocol. This is especially useful for clusters which have or plan to upgrade to 6Gb/s RAID controllers – their throughput will be increased when connected to a 6Gb/s switch rather than to a network.
Another advantage of switching to a DAS configuration for a cluster is it migrates the RAID controllers from the storage nodes to the compute nodes. In a NAS cluster, each storage node typically has its own RAID controller which communicates with the compute nodes through a network. In a DAS cluster with a SAS switch, the storage nodes are JBODs (“Just A Bunch Of Drives” – essentially hard drive warehouses without other computing components within their chassis) that are all accessed by RAID controllers located directly inside the compute nodes.
This configuration separates the RAID controllers from the storage drives and centralizes each of them for simpler management and improved performance. Now, as many RAID controllers as the cluster administrator decides can access any quantity of drives on separate JBOD-based storage. The process that allows this kind of interaction is known as SAS zoning and is illustrated in the diagram below:
For more detailed information about the various uses of the LSI 6Gb/s SAS switch, read their white paper about this product. As storage technology continues to evolve, new solutions such as a DAS cluster configuration with a 6Gb/s SAS switch are helping overcome the various I/O bottlenecks that hamper computing performance.