[dm-devel] RE: dm-devel Digest, Vol 18, Issue 2

["goggin, edward" <egoggin emc com>]

On Tue, 02 Aug 2005 09:37:14 -0500
"Christopher C. Weis" <ccweis gmail com> wrote

> I have a multipath SAN environment with storage controllers that are
> active/active.  However, the controllers are not active/active at the
> LUN-level without a performance penalty, meaning if two 
> servers want to
> see the same LUN (as in a clustered filesystem environment), they both
> need to be using the same controller.  I'm trying to figure 
> out a way to
> statically "order" the paths so that I can copy a config to all of the
> nodes using the CFS.
> 
> >From what I've read, in a single-server environment with controllers
> such as the ones I'm dealing with, the path_grouping_policy should be
> set to "group_by_serial", which should work fine, but in a clustered
> environment, I need to be sure that the path ordering is the same.
> 
> Are there any path_selectors, other than round-robin, that might
> accomplish this?  Any other ideas?
> 

One was is to configure each multipath to have two groups with one group
having a higher priority than the other based on whether the path accesses
the fast path controller.  The assignment of the highest priority path group
is non deterministic when using the "group_by_serial" path grouping policy.

Seems like you want to use the "group_by_priority" path grouping policy and
create and get_priority executable which when invoked will return a 1 for
fast path and 0 for slow path.  See the code for mpath_prio_emc, the
get_priority executable for the EMC CLARiiON array in
multipath-tools/path_priority/pp_emc/pp_emc.c.