Re: dm core patches

[Heinz Mauelshagen]

On Fri, Feb 13, 2004 at 03:39:36PM +0000, Joe Thornber wrote:
> On Fri, Feb 13, 2004 at 04:12:14PM +0100, Lars Marowsky-Bree wrote:
> > On 2004-02-12T20:13:40,
> >    Joe Thornber <thornber@xxxxxxxxxx> said:
> > 
> > > I think the main concern now is over the testing of paths.  Sending an
> > > io down an inactive path can be very expensive for some hardware
> > > configurations.  So I'm considering changing a couple of things:
> > > 
> > > - Only ever send io to 1 priority group at a time (even test ios).
> > >   To test the lower priority groups we'd have to periodically switch to
> > >   them and use them for a bit for both test io and proper io.
> > 
> > You are missing the obvious answer:
> > 
> > - Periodically checking paths is a user-space issue and doesn't belong
> >   into the kernel. User-space gets to handle this policy.
> 
> Yes, that is obvious, I had wanted to do failback automatically.  But
> pushing it to userland does allow people to write hardware specific
> tests.  I'll try it and see what people think.

Right, such policy belongs to userpsace it seems.

The reason why I put it into the multipath target is to cover the case,
where all paths are inoperational, the system is OOM _and_ the only
chance to recover from that is the hope to unfail a path in order to
release memory preasure.

'Sorry, userspace test handler can't run, your enterprise server
is a pile of sh..' is not acceptable in case there's a path we
could unfail IMO.

Regards,
Heinz    -- The LVM Guy --


> 
> Thanks,
> 
> - Joe
> -
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Heinz Mauelshagen                                 Red Hat, Inc.
Consulting Development Engineer                   Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@xxxxxxxxxx                            +49 2626 141200
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