[dm-devel] Getting device-mapper failure notifications

[Hannes Reinecke]

On 02/24/2016 01:00 PM, Andy Grover wrote:
> On 02/01/2016 11:07 PM, Avishay Traeger wrote:
>> Hi all,
>> I have a system where various configurations are possible - iSCSI/FC,
>> single paths and multiple.  For multiple I of course use device-mapper.
>> I was wondering if it was possible to:
>> 1. use it for cases where I have a single path.
>> 2. create a monitoring process that can take some action (e.g., send a
>> notification via message queue) in the case of some failure that would
>> normally cause failover.
> 
> Does dm-multipath support a single path? I don't know...
> 
Pshaw.
Of course it does.

(Might be that RH has some magic disallowing that, but certainly there's
nothing in the source which forbids it. In fact I recommend it when
using iSCSI)

So I recommend to always use dm-multipath and listen to uevents.

> but for your #2, dm-multipath publishes a uevent when a path fails,
> maybe the process could look for that? Using libudev?
> 
Alternatively (if you don't want the failover to happen from multipath
itself) you can implement your own device_handler sending out an uevent
and waiting for some magic sysfs attribute to be written to before
completing.

Should be rather trivial.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
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