Emulex Corp. this week unveiled Flash Services for its Fibre Channel (FC) host bus adapters (HBAs), including priority...
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queuing for quality of service and in-band FC message passing.
The features are part of Emulex's Gen 5 FC platform. Gen 5 is the term Brocade, Emulex and QLogic have adopted for 16 Gbps FC networking devices.
The new services to optimize HBA performance include Emulex ExpressLane and CrossLink technologies. ExpressLane is designed to enhance QoS for data in flash cache by tagging associated LUNs to give flash traffic precedence. This can reduce congestion caused by mixing flash and hard drives on storage devices.
CrossLink provides in-band FC message passing to improve communication between server nodes. The goal is to eliminate dropped packets by using the lossless FC protocol.
ExpressLane: It's a matter of priorities
ExpressLane takes advantage of a FC standard called Class Specific Control (CS_CTL), which allows for the designation of priority. Emulex HBAs will set the CS_CTL control bit to prioritize traffic. FC switches will see this CS_CTL bit and will be able to account for it in its prioritization scheme. If the switch has traffic coming from two hosts, it can favor the priority traffic between them. If the switch QoS is turned off, the switch will pass through the CS_CTL bit, said Mike Jochimsen, Emulex's director of product marketing.
George Crump, president of the Storage Switzerland analyst firm, said setting QoS at the HBA solves a congestion point problem at the link between HBA and FC switch.
"While we have had some form of prioritization for some time at the switch level using buffer credits, we have not had the ability to do this at the HBA level, at least in Fibre Channel," he said. "I would call this an important evolutionary step."
CrossLink improves east-west traffic
CrossLink ensures the communication between servers is done in FC rather than going in-band to Ethernet, which is not a lossless protocol and drops packets. CrossLink uses a type-length-value (TLV) element to communicate to the new destination server using metadata that prefills the cache.
"CrossLink is ideal for what is commonly called east-west traffic, or server-to-server communication," Crump said.
Crump said this comes into play during virtual machine (VM) migrations with server-side caching turned on. Cached data or metadata associated with the VMs should move with the VMs but that requires consistent low latency communication between servers. Ethernet does not provide that, but CrossLink enables the migration over FC.
Emulex's Jochimsen said the flash services were developed to help solve issues caused by the proliferation of flash and server virtualization in the data center. These problems can impact HBA performance.
"When you have multiple server reads on cache, using VMware vMotion and Microsoft Live Migration, you have more virtual machines between physical servers," he said. "When that happens, you have data in cache at the same time sharing multiple VMs. That's mechanically inefficient. That means the new VM has to go to the storage. It's a performance impact on the VM."
Emulex plans to include the Gen 5 FC Flash Services as part of its OneCommand Manager software in the first quarter of 2014.