[dm-devel] RE: dm-devel Digest, Vol 18, Issue 2
christophe varoqui
christophe.varoqui at free.fr
Wed Aug 3 18:50:35 UTC 2005
> >
> > 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.
> >
> Yes, also note "group_by_priority" path grouping policy may be
> overkill
> for the context. PG produced by "group_by_serial" can be
> sorted with an
> adequate prioritizer too.
>
> Does this mean that "group_by_serial" utilizes a
> "default_prio_callout" program/script as well, or is there another
> callout (or something totally different that I'm missing)?
>
Path prio are fetched in the path discovery phase (via callout, or
defaulting to 1 if no callout specified).
PG policies just decide the path grouping.
There is a implicit notion of PG prio, which is sum(path pio).
group_by_prio is special here : it's a mean for admins to implement a
new pgpolicy without having to hack the tools ... just with shell script
as prio callouts.
Regards,
--
christophe varoqui <christophe.varoqui at free.fr>
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