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

[christophe varoqui]

>         >
>         > 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>