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using LVM on a cluster


I am in the process of setting up a small 2-node HA cluster (for NFS,
active/passive) with a shared disk for storage. Because Corosync and
pacemaker look nice and good, I am trying to make it work with this
combination instead of cman, which is what clvm is compiled for in Debian.

There are a couple of howto's on the web on recompiling the lvm package
with Openais or Corosync , so that's what I did. However, I'm still
confused about the relationship between the cluster manager and the lock
manager. If I understood right, this is the correct order in which
things will be started:

* start Corosync (or openais, if clvm is compiled with openais support
* you need to run some kind of resource manager
* the resource manager (pacemaker) must have a resource defined that is
the dlm controld - I tried starting dlm_controld at the command line,
this seems to make clvm happy but unfortunately that command has no man
* then, a bunch of files appear in /sys/kernel/config/dlm

Actually, that controld should be started by the cluster resource
manager is also something I just read on the web, and it sounds kinda
odd to me. After all, you need to run an instance on every cluster node
that accesses shared storage, right?

[[I also tried the same thing but with a clvm compiled for openais, I
read it uses another lock manager ("Lck") but I'm not sure if and how
this one is actually cluster-aware since it doesn't seem to rely on a
resource defined in the cluster.]]

[[Another thing that I find rather strange is that corosync is started
waaaay at the end of the boot process, and clvm is started at the
beginning, even if I changed the dependency of 'cman' to 'corosync' in
clvm's init script. (clvm is started in rcS.d). But that's got more to
do with lsb init scripting than with clustering, I suppose.]]

If anyone could make me wiser or more educated about any of this, I'd be
grateful :-)

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