Testing Device Failure

[Bryn M. Reeves]

On Tue, 2009-10-13 at 22:12 +0100, Dan Track wrote:
> On Tue, Oct 13, 2009 at 5:22 PM, Dan Track <dan.track at gmail.com> wrote:
> > Hi,
> >
> > I've got two SAS links to my San, I want to test failure/recovery by
> > eleminating and device node. The easiest way is to manually unplug a
> > controller link and see what happens. I'd like to know how I can do it
> > via Linux, and then re-enable the device node? I have two device nodes
> > /dev/sda and /dev/sdb.
> >
> > Thanks
> > Dan
> >
> 
> Hi
> 
> Does anyone have any thoughts on this.
> 
> Thanks
> Dan
> 

If you're using device-mapper to combine the two paths into a single
multipath device you should see a change in the output of the multipath
-l/-ll commands when you unplug the cable (and if the unplugged path was
the path that was previously carrying I/O there'll also be a change of
path groups and I/O should begin flowing over the second path).

As long as you have multipathd running the failed path should be
re-added to the multipath map when it returns and depending on the
failback settings in use will trigger another path group switch.

Regards,
Bryn.