Controller IC targets entry-level, volume servers

In a move to accelerate the transition to next-generation serial attached SCSI (SAS) storage, Vitesse Semiconductor Corp. recently developed a pair of PCI Express-based SAS RAID-on-Chip (ROC) controller ICs for the entry-level and volume server markets.

The SAS ROC controller ICs are available in two configurations. The VSC7250 features eight PCI Express (PCIe) and eight 3Gbps SAS ports, and the VSC7251 offers four PCIe lanes and four 3Gbps SAS ports. The VSC7250 and VSC7251 are pin-to-pin compatible.

The key feature of the SAS ROC controller ICs is RAID on Demand technology, which allows customers to use a single board design to meet various data protection requirements with a pay-as-you-need model that cuts development costs while speeding time to market.

"What customers like about this feature is the design simplicity and flexibilityproduct developers can use a single design to make it become a RAID 0, 1, 10 or RAID 5 or 6 system," said product line manager Michael Chang, who added that Vitesse is the first chip vendor to provide a SAS ROC controller.

"Everyone else is behind us," he said.

Since SCSI has been the dominant storage interface, a large portion of the market's infrastructure is based on the technology. SAS is the serialized version of SCSI, addressing I/O and direct attach storage requirements that traditional SCSI cannot meet.

The VSC7250 and VSC7251 SAS ROC controller ICs are suitable for several applications. They can be used as a directed attached storage controllers for workstations and servers; as storage controllers connected to expanded SAS or SATA drive arrays; as upgradeable RAID processors for workstations and servers; and, as RAID controllers for storage arrays.

Traditionally, RAID 5 implementations are done with two approaches. The hardware approach requires an external I/O processor to perform the RAID algorithm calculation, while the software approach relies on the host CPU to do the job. Most enterprise applications demand a hardware RAID approach for their RAID 5 applications for better reliability and performance compared with a traditional hardware RAID 5 design, two-chip implementation that costs roughly $100, Vitesse's single-chip product is much cheaper at approximately $50, Chang said.

The VSC7250 and VSC7251 SAS ROC controller ICs integrate a MIPS64 5Kc processor core and dedicated RAID hardware acceleration engines. The embedded processor performs RAID calculation, volume rebuild and numerous interrupt requests related to I/O processing to free up the host CPU for other processor-intensive tasks.

The VSC7250 and VSC7251 SAS ROC controller ICs also feature a RAID 5 hardware acceleration circuit, as well as DDR2 memory controller and DMA controller for optimized RAID processing.

The base implementation of the VSC7250 and VSC7251 SAS ROC controller ICs are consistent, enabling them to offer two modes: I/O controller (IOC) and ROC. The IOC mode is a cost-effective method for workstations and entry-level servers for RAID 0, 1, 10 implementations. In the ROC mode, the customer is offered dual module upgrade model. The upgrade options are 16bit only for high-performance RAID 0, 1, 10 and 64bit with ECC for RAID 5 and RAID 6. Enterprise storage system manufacturers can achieve this by adding a DIMM socket and RAID key connector.

The ability of the SAS ROC controller to run at both the IOC and ROC mode provides system vendors great flexibility for a SAS storage system design. It enables them to configure the systems to meet various data protection requirements with the pay-as-you-need hardware design. Only when the advanced RAID feature sets are required by customers will the system vendors need to enable them. This flexibility is one of the major benefits of Vitesse's latest offerings.

"Vitesse RAID controllers, with the RAID on Demand and the best price/performance ratio, accelerate the proliferation of RAID in the SAS market," Chang said.

- Ismini Scouras
eeProductCenter