gmultipath HA over iscsi/iser

[John-Mark Gurney]

Max Gurtovoy wrote this message on Sun, Jun 14, 2015 at 19:16 +0300:
> lately I was testing HA using gmultipath utility over iSCSI/iSER devices.
> I'm working on 11-current code base.
> I created 1 LUN on the target side and connected via 2 different 
> physical ports from the initiator side.
> On the initiator side I see see /dev/da0 and /dev/da1.
> I created multipath device using:
> gmultipath label dm0 /dev/da0 /dev/da1.
> Now I have new device /dev/multipath/dm0.
> I set kern.iscsi.fail_on_disconnection=1 (to fail IO fast).
> 
> Issue 1:
> -------------
> I can't run simple fio/dd traffice over /dev/da0 nor /dev/da1.
> The only traffic that possible is using the multipath device dm0.
> Is this by design ?

This is probably because geom only lets one writer open the device at
a time, and when the dm0 device is open, it blocks any other writers
to it's underlying devices...  There is a special geom debug flag that
you can set to avoid this...

> In the linux implementation we can run traffic on both block devices and 
> multipath devices.
> 
> Issue 2:
> --------------
> I run some fio traffic utility over multipath device dm0 on initiator 
> side with port toggling in a loop
> 
> Port 1 down --> sleep 2 mins (iSCSI/ISER device reconnecting meanwhile 
> with no success) --> port 1 up --> sleep 5 mins (iSCSI/ISER device 
> reconnecting successecfully)
> Port 2 down --> sleep 2 mins (iSCSI/ISER device reconnecting meanwhile 
> with no success) --> port 2 up --> sleep 5 mins (iSCSI/ISER device 
> reconnecting successecfully)
> 
> The expected result is that when the port N is down than the traffic 
> moves to the available port and continue succesfully.
> I run this test for many hours and traffic FAILED (even though there was 
> at least 1 suitable path between initiator and target).

Someone else will need to answer this one...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."