On 06/14/2012 05:47 PM, Jake Smith wrote:
So it should be resC on top of resB on top of DRBD:master. I think of
collocation as being written in the reverse order of "order"
statement. That's why resources in groups start in the order they are
written and collocate in reverse from written order.
Second and this may or may not be right (travelling so I can't check
right now). It could also be creating a resource group inside the
collocation statement.
It is creating a resource set. What I think you are saying (and
experimentation seems to support this) is that the ordering of
colocation dependencies is in the opposite direction for resources
within a resource set than it is between sets. So:
# simple colocation, no sets
colocation colo inf: A B
# A -> B
# creates one set
colocation colo inf: A B C
# C -> B -> A
# creates three sets
colocation colo inf: A B (C D) E F
# B -> A -> (C, D) -> F -> E
# also creates three sets
colocation colo inf: A B C:Master D E
# B -> A -> C -> E -> D
I...uh...don't really know what to say. Is that a bug, in that it is not
reasonable in any way? Or is it a feature, in that it can't be fixed in
a backwards compatible way?
The notion of creating a resource set when nothing in the syntax
suggests is surprising. It also makes impossible some things, like a
group with two resources and role="Master", such as example 6.17 in
"Configuration Explained" [1]. What about implementing a new syntax
explicitly notating a sequential resource group, and deprecating
previous syntax for such (more than two resources, or ":<state>")?
Also noteworthy is that "Configuration Explained" is very wrong on this
issue. It says:
"in order for any member of set N to be active, all the members of set
N+1 must also be active (and naturally on the same node); and if a set
has |sequential="true"|, then in order for member M to be active, member
M+1 must also be active."
What it should say is:
"in order for member M to be active, member *M-1* must also be active."
In the same way, the graphic is wrong.
Here's another interesting observation:
colocation colo inf: (A B C)
is not an error, but does absolutely nothing.
[1]
http://www.clusterlabs.org/doc/en-US/Pacemaker/1.1/html/Pacemaker_Explained/s-resource-sets-collocation.html
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