[TriLUG] Mutipathing under 2.6.x - udev/multipath/hotplug

[Greg Foster]

On 4/21/05, Aaron S. Joyner <aaron at joyner.ws> wrote:
> Greg Foster wrote:
> 
> >Hi Folks,
> >
> >Please excuse in advance if you've covered this already.  I'm setting
> >up some fibre channel storage for MythTV, and want to achieve either
> >'active/active' or active/passive' between the drives and the host.
> >
> >
> First, let me say, you're the first person I've ever heard of who's
> setting up FC-AL drives on Brocade switches for Myth TV...  :)  You have
> a serious TV addiction that might require professional help.
> 
> Secondly, I haven't dealt with FC-AL drives directly under Linux, so I
> can't offer any productive advice on the situation.  I've dealt with
> similar setups, but usually with other layers involved such as VMware
> ESX, or Solaris in similarly bare scenarios.  Having said that though,
> I'm very curious to hear what the end result of your investigations
> are.  Please share if you find the "best" or "most appropriate" way to
> access the drives to take care of the multipathing.
> 
> If it's any consolation, The setup I'm used to using with VMware ESX,
> Brocade switches, and IBM's TotalStorage (FAStT) disc controllers, we
> expose different LUNs with different preferred paths, in an
> active/passive setup.  I.e. some of the traffic is flowing across one of
> the paths, some on the other, and things can always fail over one way or
> the other, but it's not a truly active/active setup.  My understanding
> is this is a limitation of the controllers in the FAStT that don't allow
> active/active, but I could be wrong about that.  I suspect it may depend
> on what controllers you have in front of your discs.
> 
> Aaron S. Joyner
[snip]

The disks themselves are EMC DAE trays, so the drives are loop,
intended to go to a DPE controller.  However, with copper GBICS and a
longer cable, they sit quite nicely in my rack, and login to the
switch without issue.

On the server side, I'm currently using an LP8000 and a QLA2310.  I
have a second LP8K, but wanted to check out the Qlogic as well.  I've
seen reference to the Qlogic HBAs handling multiple path failover
themselves, but am not sure if this is included in the card itself,
kernel driver, or the offering from Qlogic.

I'm brand-new to this devmapper/UDEV stuff.  Documentation on said
elements seems skinny at best right now.

Greg.