> One thing to check though. The number of DCs is a fixed number right? You
> will always have two DCs with X hosts.
I am keeping it open in case we add other sites for some reason, but likely to remain at 2.
>
> In that case:
>
> step choose firstn 2 type datacenter
> step chooseleaf firstn -2 type host
>
> First, take 2 of the type 'datacenter' and then find the remaining hosts. But
> since you will always use size = 4 you might even try:
>
> rule sydney-ssd {
> ruleset 6
> type replicated
> min_size 4
> max_size 4
> step take ssd-sydney
> step choose firstn 2 type datacenter
> step chooseleaf firstn 2 type host
> step emit
> }
>
> This way the ruleset will only work for size = 4.
>
> Wido
>
>
> > thanks,
> > Adrian
> >
> >
> > > -----Original Message-----
> > > From: Wido den Hollander [mailto:wido@xxxxxxxx]
> > > Sent: Monday, 12 December 2016 7:07 PM
> > > To: ceph-users@xxxxxxxxxxxxxx; Adrian Saul
> > > Subject: Re: Crush rule check
> > >
> > >
> > > > Op 10 december 2016 om 12:45 schreef Adrian Saul
> > > <Adrian.Saul@xxxxxxxxxxxxxxxxx>:
> > > >
> > > >
> > > >
> > > > Hi Ceph-users,
> > > > I just want to double check a new crush ruleset I am creating -
> > > > the intent
> > > here is that over 2 DCs, it will select one DC, and place two copies
> > > on separate hosts in that DC. The pools created on this will use size 4 and
> min-size 2.
> > > >
> > > > I just want to check I have crafted this correctly.
> > > >
> > >
> > > I suggest that you test your ruleset with crushtool like this:
> > >
> > > $ crushtool -i crushmap.new --test --rule 6 --num-rep 4
> > > --show-utilization $ crushtool -i crushmap.new --test --rule 6
> > > --num-rep 4 --show-mappings
> > >
> > > You can now manually verify if the placement goes as intended.
> > >
> > > Wido
> > >
> > > > rule sydney-ssd {
> > > > ruleset 6
> > > > type replicated
> > > > min_size 2
> > > > max_size 10
> > > > step take ssd-sydney
> > > > step choose firstn -2 type datacenter
> > > > step chooseleaf firstn 2 type host
> > > > step emit
> > > > }
> > > >
> > > > Cheers,
> > > > Adrian
> > > >
> > > >
> > > >
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