Sep 18, 2017

Fibre Channel over Ethernet: Basics of FCoE in SUSE Linux

I had to apply a fix for a FCoE module in YaST, and I had no idea.

After learning a couple of things I still only have a vague idea, but I am writing it down to help my future self, my team mates, and perhaps you too.

FCoE stands for "Fibre channel over Ethernet". Apparently if you have some disk on a Fibre Channel SAN (storage area network), you can use FCoE to extend the reachability of that disk to the ethernet parts of your network. It still needs to be a kind of special ethernet (10Gb, with special network cards) but that seems less special than FC hardware.

For a better overview, including a diagram, see: SUSE Linux Enterprise Server Documentation / Storage Administration Guide / Fibre Channel Storage over Ethernet Networks: FCoE.

FCoE typically uses a virtual LAN, (VLAN, IEEE 802.1Q).

There needs to be a Fibre Channel Forwarder (FCF) between the FC and ethernet parts. It has a MAC address. Note a difference from iSCSI which works on the IP level, one layer up.

YaST helps you set things up. The rest of this article could be useful if you cannot use YaST for some reason.

SLES uses open-fcoe. On SLES-12 the package is called fcoe-utils.

fipvlan (stands for FCoE Initialization Protocol VLAN discovery) shows FCFs and which interface and VLAN they are reachable with:

# fipvlan --auto
Fibre Channel Forwarders Discovered
interface       | VLAN | FCF MAC
------------------------------------------
eth1            | 500  | 00:0d:ec:b3:ca:00

It can also --create the VLAN interface and --start up the FCoE connection, but it won't make that permanent for the next boot

To make it permanent you need to

  1. enable the FCoE service (SLE11:/etc/init.d/boot.fcoe, SLE12: fcoe.service). Under the hood it uses two programs: fcoemon is the daemon, fcoeadm is a front end (fcoeadm -p shows the pid of fcoemon).
  2. write a config file, /etc/fcoe/cfg-*IFACE*, where IFACE is
    • eth1.500 if AUTO_VLAN is no; in this case, you also need /etc/sysconfig/network/ifcfg-eth1.500, see man ifcfg-vlan.
    • eth1 if AUTO_VLAN is yes; in this case, the interface is named eth1.500-fcoe. Note the unusual -fcoe suffix!

With the config files in place, rcfcoe start (and ifup eth1.500, unless AUTO_VLAN). Then you should see the disk devices:

# fcoeadm --target
    Interface:        eth1.500
    Roles:            FCP Target
    Node Name:        0x50060160BB600160
    Port Name:        0x500601663B600160
    Target ID:        0
    MaxFrameSize:     2048
    OS Device Name:   rport-2:0-2
    FC-ID (Port ID):  0x710D00
    State:            Online

    LUN ID  Device Name   Capacity   Block Size  Description
    ------  -----------  ----------  ----------  ----------------------------
         0  /dev/sdb      16.00 GiB      512     DGC VRAID (rev 0430)
[...]

People who actually know their way around FCoE will note that I have omitted many important details. Let me know in the comments whether I should come back to this and expand on some topics.

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