[dm-devel] failover vs multibus

[Scott Moseman]

On Nov 20, 2007 8:32 AM, Tore Anderson <tore at linpro.no> wrote:
>
> > Re: default_path_grouping_policy in multipath.conf
> >
> > failover = 1 path per priority group
> > multibus = all valid paths in 1 priority group
> >
> > Does this mean that if I'm using failover I'm not going to get
> > multiple path throughput?  And, on the flip side, if I'm sending data
> > through multiple paths I'm not going to get failover support?
>
> Correct, and incorrect.  With "failover" topology only one path will be
> used at a time.  With "multibus" all of them will be - but failing paths
> _will not_ be used.  So if you have eight paths to your storage and are
> using multibus topology, load will be balanced over all eight paths.  If
> one fails, load will be balanced over the remaining seven.  And if you
> fix the failed path I/O will be balanced over all eight again.
>
> There's also the group_by_prio or group_by_serial topologies which is
> normally used in setups with an active/passive controller pair (most
> midrange gear are built in this way).  In this case I/O is load balanced
> over all the paths to the primary controller of a volume only, while the
> remaining paths (usually to a standby controller) will only be used if
> all (or enough) of the primary paths fail.
>

Hey Tore,

I tested a 'multibus' config and it performs just as I'm hoping!  :)

Thanks!
Scott