[DRBD-user] FileSystem Resource Won't Start

[Jake Smith]

Glad you got it working.  I did my best to explain why to answer your question below...

----- Original Message -----
> From: "Eric Robinson" <eric.robinson at psmnv.com>
> To: "Jake Smith" <jsmith at argotec.com>
> Cc: drbd-user at lists.linbit.com
> Sent: Tuesday, December 11, 2012 3:45:33 PM
> Subject: RE: [DRBD-user] FileSystem Resource Won't Start
> 
> Jake --
> 
> > > > Add something like this:
> > 
> > > > order o_drbd_then_group_clust08 inf: ms_drbd0:promote
> > > > g_clust08:start order o_drbd_then_group_clust09 inf:
> > > > ms_drbd1:promote g_clust09:start collocate
> > > > c_group_clust08_on_drbd_master inf: g_clust08 ms_drbd0:master
> > > > collocate c_group_clust09_on_drbd_master inf: g_clust09
> > > > ms_drbd1:master
> > 
> > > Do I really need a colocation and an order? Doesn't a colo
> > inply the
> > > order?
> > 

Why didn't I see the easy answer like Andreas did?? No :-)

> > Did you read any of the links I sent about order/collocation?
> >  They answer your question.
> > 
> > Jake
> > 
> 
> I actually did follow the links you sent and read the pages. The
> information is very brief and does not answer that specific
> question. However, the pages do contain further links to what
> appears to be more detailed information, but those links go to 404
> pages.

Fair enough - I looked quickly and I believe it used to be better explained in some older documentation.  How about Because? ;-)

I believe it goes a little something like this... 
collocate resource B on A.
Once the cluster has determined where to start A then B can start regardless of whether or not A has completed its start action.
Think of resource A as something that takes 30 seconds to start.
Then assume resource B requires it to be completely started before it can successfully start up.
Now resource B fails to start... with an exit code that non-standard because something it's looking for is missing (since resource A isn't started yet) = infinity failure on current node.
This will cause the cluster to move resource B to another node except no other nodes have resource A running which results in resource B being unable to run on any node.

Add ordering A then B.
Now the cluster will wait till A finishes starting (or for multi-state/DRBD promoting) before starting B on the same node.
Everyone is happy.

Does that make sense?

Jake