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Re: [dm-devel] 2.6.2-udm2



On Wed, Feb 18, 2004 at 03:06:45PM +0100, Heinz Mauelshagen wrote:
> On Wed, Feb 18, 2004 at 01:09:06PM +0000, Joe Thornber wrote:
> > On Wed, Feb 18, 2004 at 01:01:29PM +0100, Heinz Mauelshagen wrote:
> > > We can and will need to mlockall() the path test tool, which will make sure
> > > that we can access all pages of the tool, shared library or mmap'ed file it
> > > needs.
> > 
> > Yes, I think Christophe Varoqui who is writing the tools is aware of
> > this.
> > 
> > > But if *all* paths of the multipath target to test are failed
> > 
> > Then we error the ios, we have no choice.  The userland tester should
> > not wait until this situation before testing.
> 
> Right, but it won't have a chance to test early enough worst case.
> 
> Eg, all phyiscal paths fail because of a short power outage to multiple switches
> in a fabric, which come back online shortly later when all paths have been
> failed by the multipath target.

We ought to support both methods: allow fail or suspend when no paths are
available, and not pick one or the other in the kernel. And for now,
support whatever is easiest.

Allowing suspend on no paths available also makes dm multipath very useful
for single path cases where we want to allow hot replacement of the
transport without having to umount or shutdown users of the disk.  

For example, if you need to replace a failing cable.

-- Patrick Mansfield



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