[DRBD-user] 3-Node DRBD Without Stacking

Pavlos Parissis pavlos.parissis at gmail.com
Wed Nov 17 14:24:34 CET 2010


On 16 November 2010 18:45, Felix Frank <ff at mpexnet.de> wrote:
> On 11/16/2010 05:55 PM, Robinson, Eric wrote:
>>>> Is it possible to deploy a 3-node CRM-based cluster where:
>>>>
>>>>     -- nodes A and C share resource R1 on /dev/drbd0
>>>>
>>>>     -- nodes B and C share resource R2 on /dev/drbd1
>>>>
>>>>     -- resource constraints prevent R1 from running on node B and
>> prevent
>>>> resource R2 from running on node A?
>>
>>> I don't think I understand what you're trying to do.
>>> Please elaborate.
>>
>>> Why would you need to prevent R1 from "running" on
>>> Host B if the resource is shared between A and C?
>>> B is not at all configured to connect to R1, is it?
>>
>> It's a three-node CRM cluster where node C acts as a failover for nodes
>> A and B, but nodes A and B do not fail over to each other. However, in a
>> three-node CRM cluster, all resources are allowed to run on all nodes by
>> default. For example, even though resource R1 only physically exists on
>> nodes A and C, if node A fails Pacemaker might try to start it on node B
>> if we don't put in some kind of constraints. You follow?
>
> I think I do now.
>
> The ocf:linbit:drbd RA should be smart enough to realize that R1 is not
> configured (in drbd.conf) to ever run on R1. But don't quote me on that.
Nope, there is not such intelligence in the RC because PE takes this
kind of decisions.

>
> If you are still afraid it might take a nonsensical action and bring a
> DRBD device up on a node that is not configured to do that, feel free to
> add a constraint like
>
> location p_drbd_r1_not_on_hostB -inf: p_drbd_r1 hostB
>
> or something along those lines.
>
> HTH,
> Felix
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