Going Forward With SCSI Express
Don’t Get Stuck Riding A Dinosaur: Next-Gen Interfaces And Protocols ExplainedThere are no winners in an ongoing, protracted standards war. In a perfect world, the forces behind NVMe and SOP/SCSI Express would team up and produce a single solution. It’s not that crazy of an idea, either. Both projects have the same broad objective: establishing and standardizing PCIe as the future of enterprise storage, and several companies are partners for both technologies.
According to industry experts, NVMe has a slight lead in bringing products to market, but SCSI Express has the support of ANSI, one of the industry’s most trusted groups. What happens after NVMe’s window closes, and SCSI Express SKUs become available? There’s reason to believe that SCSI Express will emerge as the preferred technology.
A closer examination of NVMe reveals some potential weaknesses. Take for example an array caching configuration where a RAID controller puts several hard drives together with an SSD. Software finds hot spots on the HDD array and dynamically shifts the relevant data to the SSD. The RAID controller itself deals with this analysis and maintenance rather than increasing traffic through the PCIe bus or the main memory. A SAS controller does all the work in the background and is transparent to the host, and because SCSI Express uses the same protocols and procedures, SCSI Express architectures will have this advantage, too. Compare this to NVMe, which runs caching algorithms in the host. Data flows from the hard disks over the PCIe bus, through the main memory, to the SSD, and then back the other way. Each operation requires a pair of trips across the memory bus, which ties up resources that could have been spent on virtual machines, for example.
Recently the SCSI command set received a new addition, “offload data copy,” which is an extension to the “extended copy” command. When a SCSI Express SSD pairs with a SOP-based RAID controller, offload data copy operations can occur across the PCIe bus without requiring the use of system memory. This is an example of how SCSI Express has been better optimized for lower total resource impact.
Sooner rather than later, next-gen storage will be here, and it will be here to stay. Performance and capabilities should increase dramatically, but make sure you do your homework before deciding how you’ll upgrade your enterprise.
