[dm-devel] Designing a new prio_callout

[Stefan Bader]

Hi Ethan,

I might not understand the problem completely but I do not understand
the benefit of changing rr_min_io. As far as I can see from your
multipath output, both of the devices consist of two path groups with
one path. This means, as long as there is no path failure I/O will
never be sent to the inactive group.
I guess the only thing you need is a script that might find out from a
given scsi device (like sdc) whether this would be the preferred path
and then print a number that represents the priority (the lower, the
higher). Then use this as priority callout and group by priority with
failback set to immediate.

Regards,
Stefan

2007/8/14, Ethan John <ethan.john at gmail.com>:
> For the record, setting rr_min_io to something extremely large (we're using
> 2 billion now, since I'm assuming it's a C integer) solves the immediate
> problem that we're having (overhead in path switching causing poor

> > mpath45 (20002c9020020001a00151b6b46bb57b0) dm-1
> company,iSCSI target
> > [size=15G][features=0][hwhandler=0]
> > \_ round-robin 0 [prio=1][active]
> >  \_ 22:0:0:1 sdc 8:32  [active][ready]
> > \_ round-robin 0 [prio=1][enabled]
> >  \_ 23:0:0:1 sde 8:64  [active][ready]
> > mpath44 (20002c9020020001200151b6b46bb57ae) dm-0
> company,iSCSI target
> > [size=15G][features=0][hwhandler=0]
> > \_ round-robin 0 [prio=1][enabled]
> >  \_ 22:0:0:0 sdb 8:16  [active][ready]
> > \_ round-robin 0 [prio=1][enabled]
> >  \_ 23:0:0:0 sdd 8:48  [active][ready]
> >