[dm-devel] Multipath target - internals?

[Lazar Obradovic]

Hi, 

is there a document describing inner works of DM multipath target?

I did some testing and found out that detecting redundant paths works
just like it should (kudos for christophe), load-balancing too, but
detecting failed path, for some reason, does not (or perhaps it is, but
too late). 

I'm using GFS on top of multipathed virtual disk, and it seems that DM's
timeout is a bit larger than GFS's. Shutting down one port on FC switch
(thus, disabling at least one path) causes GFS to freeze and then hang
with kernel panic (reporting that /dev/sda had physical errors - if you
want, I could post logs). 

Skimming through code, I've found that DM will declare some path as
unusable after some error count / rate. Is this true and where is it
defined exacly? Can someone point me to the right direction so I could
tweak DM a bit?

-- 
Lazar Obradovic, System Engineer
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