[dm-devel] [PATCH 0/4] path latency prio fixes

[Martin Wilck]

On Mon, 2017-12-04 at 22:23 +0800, Guan Junxiong wrote:
> 
> > An open question is what multipathd should do wrt path grouping if
> > it
> > only has preliminary prio values, in particular with group_by_prio.
> 
> For the open question, in this situation, IMO  it's reasonable to
> overwriting
> the preliminary prio values if we let the user/admin know : "this is
> an
> asynchronous priority checkers and it has high priority to the other
> synchronous
> prioritizer.

This is not what I meant. Once we have the final prio values, it's of
course the right thing to overwrite anything preliminary. 

The "open question" arises at the time when we only have the
preliminary values: We may group paths wrongly. Really bad example: we
might be putting active and passive paths of a storage system into the
same path group, causing endless trespassing... we should probably use
"failover" policy if "group_by_prio" is selected but no reliable
priorities are available.

Martin
-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)