by: Gary Gumanow
EXTENDING NETWORK STANDARDS
10 Gigabit Ethernet (10GbE), standardized by the IEEE in 2004, delivers ten times the bandwidth of previously available networking technologies, and its availability has prompted the development of new standards for the data center, delivering on the promise of a single networking fabric or technology to connect storage, the LAN, and Inter-Processing Communication, or IPC.
These new IEEE standards go by several names: “Converged Enhanced Ethernet,” “Data Center Ethernet,” and the industry-standard term “Data Center Bridging,” or DCB. In this series of blogpostings we provide an overview of the reasons DCB is being developed and how it can improve networking in the data center for applications, servers, and storage.
ETHERNET RELIES ON TCP FOR “LOSSLESS” COMMUNICATIONS
Many IT managers deploy their networks to be “lossless” by over-provisioning bandwidth so all network applications can operate at their desired bandwidths. However, networks are dynamic organisms, change over time, and most likely have changed once rolled out. IT managers don’t plan for their networks to drop packets from inception and therefore having inherent mechanisms to recover from them are a necessity.
While Ethernet is generally a reliable technology, data packets can be dropped in transmission due to network congestion, traffic load balancing, over-subscription, and loads on servers and switches. Dropped packets don’t cause big problems, but they can result in performance variations for applications.
Protocols, such as TCP (TCP/IP), run on top of Ethernet to ensure seamless communications. TCP will take note if packets are dropped during communication, and if so, those packets are re-sent, but if not, confirmation of a completed transmission is returned. With this “handshake,” TCP delivers “lossless” communications. TCP also provides a dynamic flow control mechanism, called windowing, which essentially elasticizes the two ends of a buffered connection based on the capabilities of those endpoints. Finally, TCP provides routing capabilities so that communications work seamlessly across routed and different networks. In a converged Ethernet environment, storage network technologies that do not have a built-in recovery mechanism like TCP, require safeguards against dropped packets. Enter Data Center Bridging, the most recent set of IEEE standards that provide this enhancement to Ethernet.
The next blogpost in this series will focus on some of the benefits of DCB and what makes it so compelling for storage in today’s data centers.
If DCB provides the benefit to your SAN as promised, what percentage improvement in performance would you need to see in order to implement a change to the infrastructure for DCB?
Are you seeing issues today with performance and TCP retransmits?