Joy Jiang and Claudio DeSanti, The role of FCoE in I/O consolidation, Proceedings of the 2008 International Conference on Advanced Infocomm Technology
Summary of Paper
The paper describes the rational for adopting FCoE protocol as a way to I/O consolidation at the datacenter level. Specifically, FCoE describes running Fibre Channel over 10GB Ethernet, and thus provides seamless integration with existing Ethernet infrastructure and packet encapsulation of FC traffic that does not require maintaining stateful gateways for existing FC infrastructure. Replacing separate Ethernet, FC, and possibly Infiniband adapters in the servers by dual CNAs that can carry FCoE traffic and reducing cabling requirements provides substantial cost savings.
Summary of Class Discussion
- Storage marketplace is close to $2.5 bln
- Hard drive performance is limited by physics, needed a way to consolidate multiple devices and have them appear as a single high-performance device
- FC technology was developed to be a hardware engineer answer to networking: simple to implement in hardware on the lowest level, many layers higher up, some of them never implemented at all
- FC0 uses point-to-point links and a concept of credits in lieu of TCP windows, life without dropped packets (to the point of crashing Windows since handling of dropped packets was never implemented)
- Current error rates on fiber are 10^{-17}, but with twisted pair media they can go up to 10^{-12}
- IBM has a hard drive with built-in CRC, so the blocks are 528 bytes and FC supports that
- 1Gb FC is actually 800Mb/sec, 1Gb Ethernet is just that
- FC zones provide security
- Credit = line delay / packet size
- FC allows multipath (FC Shortest Path First)
- FC has ambiguous standards, interoperability is a nightmare, single vendor setups are common, Cisco is an OEM
- ‘Pause’ frame was used to help with flow control after a standards negotiati0n
- iSCSI is more adopted in greenfield installations
- FCoE wins over other approaches due to having a stateless gateway
- FCoE frame has a lot of padding so that its size does not need to be known in advance to allow on the fly switching
- End-to-end argument still works and it does show that making network smarter does increase its performance
Opinion/Critique
The paper is written by a team from Cisco (working on the FC hardware) and Finisar (working on Xgig hardware analyzer) so it mostly reads as a marketing white paper. The figures that look like they came from a marketing presentation enhance this impression. Overall paper makes a good point about investment protection and future cost savings, so if the hardware is indeed delivered the FCoE’s future does look bright.
