[dm-devel] setup Pathpriority manually

[Hannes Reinecke]

Chandra Seetharaman wrote:
> On Thu, 2007-06-21 at 20:13 +0200, Markus wrote:
>> Hi,
>>
>> i do have an active-passive Storage where the LUN could be used by
>> both Controllers but one is bloody slow. I tried all
>> /sbin/mpath_prio_* ways do determin which is the "active" one but none
>> of them worked. Is there a way to set this manually? Is there a
>> different way to determin which is which rather than using the
>> existing Commands?
> 
> If your device is not one of the supported devices, you can ask the
> vendor about how to determine the active and passive paths.
> 
> mpath_prio_tpc is a good example of how the active/passive device
> information is used to determine the path priority.
>   
Yes, but this assumes that documentation about the device is available.
That is not always the case (no NDA, uncooperative Vendors, or Vendor
gone out of Business etc.)

There is actually an easier way to do this: As all the mpath_* callouts
are in fact standalone programs, so you can easily supply your own callout.
Just write a small shell script which takes the device name as input.
The priority is just the return value of that program; the path with
the highest priority will take precedence over all the others.
Paths with identical priorities will be grouped into a path group if
the policy is set to 'group_by_prio' (which I would recommend if a
priority callout is specified).
The task of figuring out the physical location of a controller by
specifiying the device node is left to the reader.
But relying on udev here might be dangerous as multipathd might run
in parallel to udev.

HTH.

Just out of curiousity: Which machine is that?
Would be an idea to put that into the hardware table, if only with
a large fat
"Don't use that array unless you know what you're doing"
kinda-thing warning.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)