Thursday, July 2, 2009

FCoE or iSCSI? that is the question.


I found a great article today to help people decide whether to go with FCoE or iSCSI, or when each technology fits best. Bellow are some snippets, and here's the link to the full article.

The arrival of Fibre Channel over Ethernet (FCoE) makes it possible to consolidate on an Ethernet fabric to meet both storage and local area network needs. However, it also means that you now have two SAN options for use on Ethernet networks: FCoE and iSCSI. This raises obvious questions about what the differences are and when you should choose one versus the other.

The FCoE layer replaces the TCP/IP layer used in iSCSI and also requires the Data Center Bridging (DCB) Ethernet improvements. The DCB working group of the IEEE has extended IEEE 802 standards to satisfy the requirements of different traffic classes on a single network without creating “traffic interference,” that is, without having one class of traffic starve another.

Since FCoE was designed without the Internet Protocol (IP) layer, it is not intrinsically routable using IP. However, FCoE routing can be performed using already established protocols such as FCIP.

The iSCSI protocol can be implemented in networks that are subject to packet loss, and iSCSI can run over 1 Gigabit Ethernet (1GbE). FCoE requires 10 Gigabit Ethernet (10GbE) and a lossless network with infrastructure components that properly implement pause frame requests and per-priority pause flow control (PFC) based on separate traffic classes that map to different priorities. The idea behind PFC is that during periods of congestion, high-priority traffic is allowed to continue while lower-priority traffic is paused.

Your 10GbE switches will need DCB support for FCoE, including a range of enhancements for classes of service, congestion control, and management. FCoE also requires Jumbo Frames because the FC payload is 2,112 bytes and cannot be broken up; iSCSI does not require Jumbo Frames.

While FCoE may create some confusion in the short term as you take steps to decide if and where it makes sense in your infrastructure, the long-term benefits are clear. By consolidating your networks on a single Ethernet fabric you can dramatically reduce capital and network management costs without sacrificing the ability to choose the protocol that makes the most sense for your application set.

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