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A TOE in the water

Stuart McRobert

A few years ago many network switch vendors replaced software based routing engines in their products with hardware ASICs capable of operating at wire speed gigabit Ethernet line rates. In addition these ASICs provided a rich set of additional features and benefits, e.g. QoS, low latency, etc. with little or no performance penalty for the user.

Meanwhile host based network interface cards (NICs) have increasingly become more intelligent, allowing some of the more CPU or kernel IO intensive tasks to be done by the network card itself (checksums, TCP Segmentation Offloading (TSO), IPsec and triple DES, etc.).

Today modern PCs can easily achieve fast Ethernet line rates, but find anything like sustained gigabit Ethernet rates much more of a challenge and very CPU intensive. Some reports indicate that for each Gbit of networking throughput a GHz of processing power has been required.

However with increasing network traffic rates forecast, and an interest in moving storage away from specialist vendor specific fibre channel SANs to generic IP storage networks (iSCSI), vendors are starting to provide hardware based ASIC TCP Offload Engines (TOEs). Like those used in network switches, these can easily approach wire speeds, initially Gigabit Ethernet but with 10 Gigabit as the next obvious step, whilst significantly reducing host CPU overheads by offloading the entire TCP stack to the on-board ASIC instead. Useful for both intensive TCP/IP networking and evolving iSCSI, or internet SCSI, which is an IETF standard mapping SCSI storage blocks into Ethernet IP packets.

This talk will cover these interesting topics and report on our initial experiences with TOEs under Linux.


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