On Thu, 5 Jul 2012, Mark Kirkwood wrote:
> Hi,
>
> I am experimenting with ceph (rbd only for now), and have a few questions
> about what is possible via placement rules.
>
> For example I am looking at a setup with a local datacenter (datacenter0) and
> a remote one (datacenter1). I'm using a placement rule:
>
> rule rbd {
> ruleset 2
> type replicated
> min_size 1
> max_size 10
> step take datacenter0
> step chooseleaf firstn -1 type host
> step emit
> step take datacenter1
> step chooseleaf firstn 1 type host
> step emit
> }
>
> and I have the rdb pool set to size 3.
>
> So I *think* I am saying I want 2 replicas in datacenter0 and one in
> datacenter1 [1].
That's right!
> The questions I have are:
>
> 1/ I would like to be able to have a way to say something like: Make 2 copies
> at datacenter0, 1 at datacenter1 - wait for the ones at datacenter0 to be
> written but not the ones at datacenter1 (so asynchronous for the latter). Is
> this possible, or planned?
It is not possible yet, but planned for the future.
> 2/ Also I would like to be able to say make my number of copies 3, but if I
> lose datacenter0 (where 2 copies are), don't try to have 3 copies at
> datacenter1 (so run degraded in that case). Is that possible?
That is what you get now. Doing the opposite (2 copies in DC1, 1 in DC2,
but if DC2 is down 3 in DC1) is not currently possible with the crush
rules.
sage
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