[DRBD-user] HA cluster drbd-attr resource agent

[Ivars Strazdiņš]

Hi DRBD experts,
what are advantages of using drbd-attr resource agent in RedHat HA cluster vs “simple" resource constraint?
We have a SAN backed DRBD volume that is replicated from one HA cluster to another.
DRBD User Guide in paragraph 7.7 describes how to use drbd-attr resource agent to setup location constraint so that resource that depends on DRBD does not start before DRBD is promoted.
But in my tests same result can also be achieved by setting a resource constraint as below and not involve any rules that use drbd promotion score.

pcs constraint order promote DRBD-volume-master then DEPENDENT_resource score=INFINITY 

Do I miss anything crucial here?
Thanks in advance for any opinion.
With kind regards,
Ivars Strazdins
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