[Linux-cluster] Linux Cluster + KVM + LVM2

[Ralph.Grothe at itdz-berlin.de]

Hi Marc,


though Digimer's RHCS tutorial is an excellent introducion to the
RHCS cluster with a thourough step by step reference to setting
up a Xen cluster, and I'd highly recommend you read it, you
probably also would like to have look at these articles in the
cluster wiki which focus a little more condensed on your
questions.

Here is described how to set up so called HA-LVM which avoids the
clmvd overhead and is for settings like yours where you only
require active/passive VG activation (i.e. a shared storage VG is
only activated on a single cluster node at any time). 
This is achieved by tagging of the affected VGs/LVs.

https://fedorahosted.org/cluster/wiki/LVMFailover

Unfortunately, this article lacks mentioning of the required
locking_type setting in lvm.conf.

But if you have access to RHN this article on HA-LVM does, and it
also outlines both methods, i.e. the so called "preferred clvmd"
method and the so called "original" (or what I'd call "tagging")
method which doesn't require clvmd:

https://access.redhat.com/kb/docs/DOC-3068


Should you on the other hand require active/active VGs (i.e.
simultaneous activation of the same shared VG on more than one
cluster node), which I consider not a requirement for a KVM
cluster (but I lack any experience in this field) the recommended
procedure is described here:

https://access.redhat.com/kb/docs/DOC-17651


Important aside, after you've edited the lvm.conf you are
required to make a new initial ramdisk (or at least touch the
mtime of the current initrd) or cluster services won't start on
that node (watch entries in messages or whereever syslogd logs
clulog stuff to).



In this article you may find something treating KVM VMs'
migration.

https://fedorahosted.org/cluster/wiki/KvmMigration



Regards
Ralph
(an RHCS newbie himself)
________________________________

	From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com] On Behalf Of Marc
Caubet
	Sent: Tuesday, July 19, 2011 4:19 PM
	To: linux-cluster at redhat.com
	Subject: [Linux-cluster] Linux Cluster + KVM + LVM2
	
	
	Hi,
	
	we are testing RedHat Cluster to build a KVM
virtualization infrastructure. This is the first time we use the
Linux Cluster so we are a little bit lost. Hope someone can help.
	
	Actually we have 2 hypervisors connected via Fiber
Channel to a shared storage (both servers see the same 15TB
device /dev/mapper/mpathb).
	
	Our idea is a shared storage to hold KVM virtual machines
by using LVM2. Both server should be able to run Virtual Machines
from the same storage, but we should be able to migrate or start
virtual machines on the other server node on crash.
	
	So the plan is:
	
	- Virtual Machine image = Logical Volume
	- CLVM2 cluster: only one server node at the same time
will be able to manage the volume group-
	- KVM Virtual Machine High Availability. Machines will
run on one server node. If for some reason the server node
crashes, the second will start / migrate the virtual machine.
	
	Basically we woul like to know:
	
	- How can we create a cluster for the LVM2 shared storage
(when we create it, it does not work since both server nodes have
the VG as Active)
	- How can we create a cluster service for a virtual
machine (we guess it has to be done 1 by 1)
	- Since we have 2 server nodes, how to increase the
number of votes for quorum (qdisk over a heartbeat logical volume
partition?)
	
	Thanks and best regards,
	-- 
	Marc Caubet Serrabou
	PIC (Port d'Informació Científica)
	Campus UAB, Edificio D
	E-08193 Bellaterra, Barcelona
	Tel: +34 93 581 33 22
	Fax: +34 93 581 41 10
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