Multipath-Tools -- Priorities to different paths?

Fabio Massimo Di Nitto fabbione at
Fri Aug 10 06:19:19 UTC 2007

Hi Christian,

Christian Brandes wrote:
> 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?

You can use any kind of script you want. It's enough it prints to stdout an
integer that specifies the priority for that device.

prio_callout   "/bin/foo %d"

your script will be called with:

foo /dev/sdX

then you just echo $priority and exit 0.

In your specific case I would probably also consider two options:

- reconfigure the SAN to support multibus (each controller access the disks
independently instead of bouncing around to the active controller)

- change the multipath path_selector option to non-round-robin.

Anyway those kind of changes are really strictly related to your setup. Just
make sure that the foo callout is highly safe if opt for that direction.

As a side note.. you also need to make sure that the script is available when
udev is about to re-execute the rules after initramfs device poking. so it needs
to be in /bin or /sbin but there is no need to have it in the initramfs itself.


I'm going to make him an offer he can't refuse.

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