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Accelerate Performance with Seamless Networking Consider the network adapters for iSCSI. Traditional


network adapters can impose significant processor overhead. This might not seem like a major concern for today’s multicore processors, but there are several technologies available to ease processor overhead and vastly improve iSCSI performance, especially when mixing storage and non-storage traffic on the same LAN. The best approach is to adopt enterprise-class “offload-capable” network adapters that provide TCP/IP offload or iSCSI offload capabilities.


TCP/IP offload capabilities are not new—in essence,


the “offload” implements the TCP/IP stack in the network adapter’s hardware, alleviating those tasks from the processor. Many modern network adapters implement the more recent Microsoft TCP Chimney offload architecture available in all versions of Windows Server 2008, which also handles IPv4 and IPv6 connections. However, TCP Chimney may not be compatible with Hyper-V. TCP/IP offload-capable NICs are available for GbE and 10GbE, and will help accelerate all types of network communication.


Similarly, network devices with iSCSI offload


capabilities include their own iSCSI initiator hardware on the adapter that handles iSCSI traffic specifically. Host bus adapters with iSCSI offload are available for GbE and 10GbE LANs.


Optimize Processes to Reduce Overhead and Increase Efficiency Enable jumbo frames for iSCSI. Use network devices


(adapters, switches, routers, storage targets, and so on) that support jumbo frames. A normal Ethernet frame encapsulates a 1,500-byte payload in addition to the overhead of the frame. The overhead helps systems sort and reorder the frames and request resends when frames are missing or damaged. As a consequence, a great many individual frames (and a substantial amount of overhead) may be needed to transfer a file or other data across the network.


Jumbo frames allow a much bigger data payload in


each Ethernet frame, and typical jumbo frames may transfer 4,000, 9,000, or even 14,000 bytes of data in each frame. This means the amount of overhead versus the data is much smaller, making the data exchange more efficient. However, each physical and virtual element in the network must support the same jumbo frame size. If not, noncompliant components will need to be upgraded (or the frame size adjusted) to achieve end-to-end compatibility.


Take Advantage of Multi-Core Processing Power Adopt Receive-Side Scaling technology. You’ve already


seen that TCP/IP can place a burden on a processor, but an additional problem is that TCP/IP uses the same one processor core—it does not spread out the workload among multiple cores. This is due to the legacy design


of the TCP/IP stack (from the days of single-core processors). Receive-Side Scaling (RSS) capability in the network adapter overcomes this problem by balancing incoming network frames across various processor cores. It is not a critical technology (especially if offload-type adapters are used) but it is strongly encouraged as a best practice for iSCSI.


Segregate the storage and LAN traffic. Although iSCSI


allows storage and regular LAN traffic to share the same physical network, some organizations may still opt to separate the storage and non-storage traffic using virtual LANs (VLANs) or separate physical networks. This is particularly important in GbE LANs, but may not be essential in all 10GbE networks.


For example, a VLAN allows a single physical network to


be segregated into two or more logical networks. This is an ideal means of separating storage traffic from non-storage traffic, ensuring that storage traffic is only available to the server and storage subsystems.


It is also possible to create a separate physical LAN that


is dedicated to storage traffic. This would include separate network adapters, cabling, switches, and so on. This is the costliest option because the physical LAN elements are duplicated, but it also supplies full network bandwidth to storage. It also provides the best security because there is no chance for storage and non-storage data to mix on the same wires.


ABOUT THE AUTHOR: Stephen J. Bigelow, Senior Technology Editor in the Data Center and Virtualization Media Group at TechTarget Inc., has more than 20 years of technical writing experience in the PC/technology industry. He holds a bachelor of science in electrical engineering, along with CompTIA A+, Network+, Security+ and Server+ certifications and has written hundreds of articles and more than 15 feature books on computer troubleshooting, including Bigelow’s PC Hardware Desk Reference and Bigelow’s PC Hardware Annoyances.


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