Multipath-Tools -- Priorities to different paths?

[Christian Brandes]

Hi,

I have got an Ubuntu Server, that sees 1 Volume over two fibre channel 
paths, e.g. /dev/sdd and /dev/sde.

With multipath-tools I can create a device in /dev/mapper that uses both 
paths. Generally there is the possibility to set priorities. At the 
moment priorities are the same, and the first path found is used. But it 
varies which is found first.

I would like to set different priorities to configure which path should 
be prefered. Does anyone know how to do this?

I know, there is 
/usr/share/doc/multipath-tools/examples/multipath.conf.annotated.gz

An Option "prio_callout" exists to call out a script to determine path 
priorities.
But there is neiter an explanation how it should work nor an example 
prio_callout-script.

Does anyone have further information how to set these path priorities?

In my special case I have a dual port HBA in my server. That has one 
port directly connected to controller A of a storage system and the 
other one to controller B. Disk drives are handled by controller A and 
failed over to Controller B if A dies. When both controllers are alive, 
B can serve disk access too, but it does it by handing it over to A. So 
path B is much slower than A.

Current output of "multipath -ll":

3600d0230ffffffff0014a77581600f00dm-10 IFT,F16F-R4031-6
[size=195G][features=0][hwhandler=0]
\_ round-robin 0 [prio=1][active]
  \_ 0:0:0:0 sdd 8:48  [active][ready]
\_ round-robin 0 [prio=1][enabled]
  \_ 1:0:0:0 sde 8:64  [active][ready]


My aim is to identify which path is the one connected to controller A 
and then set the other one a lower priority, in order to let the server 
first use path A and only in case of a failure use B.

The output of "multipath -ll" should be something like:

3600d0230ffffffff0014a77581600f00dm-10 IFT,F16F-R4031-6
[size=195G][features=0][hwhandler=0]
\_ round-robin 0 [prio=1][active]
  \_ 0:0:0:0 sdd 8:48  [active][ready]
\_ round-robin 0 [prio=2][enabled]
  \_ 1:0:0:0 sde 8:64  [active][ready]

I would be glad about your help.

Best regards
	Christian