FCoE storage: Fibre Channel over Ethernet explained

Misc

FCoE storage: Fibre Channel over Ethernet explained

Fibre Channel over Ethernet (FCoE) is a transport standard that takes Fibre Channel (FC) frames and encapsulates them within an enhanced Ethernet network. FCoE retains Fibre Channel upper-level protocol features such as data integrity checking and flow control, but not its cables and interfaces.

Fibre Channel is designed as a channel interface. That is, it guarantees lossless delivery of frames with a predictable latency. FCoE brings these qualities to the (to date) inherently less-reliable Ethernet environment.

FCoE further reading
FCoE special report

Will FCoE bring a fabric product shakedown? 

Brocade, Cisco disagree over FCoE adoption rate

 

Does FCoE run on standard Ethernet? 

No. Standard 10/100, 1 Gb or 10 Gigabit Ethernet (10 GbE) isn't a lossless technology and doesn't have the functionality -- flow control, guaranteed delivery, etc -- associated with a channel interface like parallel SCSI, Fibre Channel, FICON or ESCON.

Instead, FCoE runs on versions of Ethernet that have been improved to provide low latency, quality of service, guaranteed delivery and other functionality traditionally associated with channel interfaces.

Currently, vendors in the space have different names for their versions of this enhanced Ethernet. Cisco Systems refers to it as Data Center Ethernet (DCE) , while Brocade, IBM and everyone else calls it Converged Enhanced Ethernet (CEE).

Over time, the two camps will likely settle on one standardised approach.

FCoE benefits

FCoE allows organisations to use Ethernet cabling for data centre network and storage traffic. This will potentially remove the need for a discrete Fibre Channel fabric.

As well as reducing the amount of cable, the number of interface cards required will also potentially halve. Instead of separate Ethernet network cards and Fibre Channel host bus adapters (HBA), the two functions will be combined onto a single converged network adapter (CNA). The CNA deals with both protocols on a single card, while allowing storage and network domains to be controlled independently.

In addition, FCoE will likely offer much higher bandwidth much sooner than Fibre Channel. While Ethernet speeds of 40 Gbps and 100 Gbps are in the pipeline, Fibre Channel currently tops out at 8 Gbps, with plans to increase that to 16 Gbps being the only ones on the table.

The rationalisation of network infrastructure that comes with FCoE means fewer devices and cabling will be required, which this brings the potential to cut equipment, power and cooling costs.

Status of FCoE standards

Last June, FCoE passed a key milestone when it was approved as a standard by the FC-BB-5 group of the T11 Technical Committee. FCoE is currently on its way to being confirmed by International Committee for Information Technology Standards (INCITS) as an American National Standards Institute (ANSI) standard.

Some aspects of the standard are still a work in progress, however. Enhancements to the Ethernet side are still being worked on by the Institute of Electrical and Electronics Engineers (IEEE), while aspects of the Fibre Channel component are still being finalised. Following final development of the standard, there will likely be a time lag until ratification.

Available FCoE products

You can buy FCoE CNAs and some FCoE-capable top-of-rack switches. What you can't buy are FCoE director switches. That means you can't yet build a converged data centre infrastructure based on a core-edge topology with Ethernet and FCoE.

The transition to FCoE: How do vendor roadmaps differ?

The two key storage switch vendors -- Brocade and Cisco Systems -- differ on the likely pace of transition to FCoE. Brocade forecasts slower progress than Cisco Systems.

That stance is reflected in the incorporation of FCoE into products, with Cisco Systems more bullish in this regard. It has offered pre-standard FCoE in some top-of-rack switch products, but FCoE won't be available in the firm's MDS 9500 directors and Nexus 7000 Series switches until the standard is fully ratified.

Brocade, meanwhile, supports pre-standard FCoE and CEE in its Brocade 8000 switch and in the FCoE 10-24 blade switch that fits into its DCX Backbone.

Which storage vendors have made a move on FCoE? 

NetApp has stood out among storage vendors with its claims to be the first to offer "native FCoE". A number of its NetApp FAS devices -- the 6000 Series, 3100, 3040, 3070 and 2050 -- incorporate FCoE in a QLogic converged adapter.

NetApp claims some customers already run FCoE, but in the absence of core/director switches with FCoE there will be questions over the scalability of such deployments, which must be restricted to server top-of-rack switch storage in terms of architecture.

EMC plans to offer native FCoE ports on its Clariion arrays in 2010. EMC has said it's in no rush to support FCoE because of the architectural limitations that exist until FCoE-capable directors arrive.

 

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This was first published in May 2010

 

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