[dm-devel] [PATCH 3/3] multipathd: Add 'sysfs' prioritizer

[Hannes Reinecke]

On 11/08/2016 07:52 PM, Xose Vazquez Perez wrote:
> On 07/15/2016 08:48 AM, Hannes Reinecke wrote:
>
>> Recent kernels have an 'access_state' attribute which allows
>> us to read the asymmetric access state directly from sysfs.
>
> Hi Hannes,
>
> with this patch it's impossible to select/autodetect ALUA.
> sysfs always takes precedence over alua.
>
> "detect_prio no" was added to overrides section, to make
> it work again.
>
> SLES 12-SP2
>
> Thank you.
>
But this was precisely the idea.
(After all, it says 'auto-detect', right?)

For ALUA-capable arrays we have a reliable priority detection with the 
ALUA device-handler.
So it's far preferable to use the sysfs-provided information (as they 
are populated by the ALUA device-handler); the ALUA prioritizer in 
multipath-tools will be used as a fallback in case the device handler 
isn't loaded or the sysfs files are not present.
Using the sysfs handler has the neat side effect that you don't need to 
do I/O for detecting the priority, thereby eliminating one possible 
cause for multipath being stuck during failover.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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