[Linux-cluster] Cluster and LVG/LV

[Jeff Sturm]

Okay.  For CLVM it probably makes the most sense to run one big volume
group across your cluster, but there's also the option of running a
non-clustered LVM on each Dom0 host.  The latter would only work for you
however if you don't require Xen migration.
 
I see 3 options for central storage in a Xen cluster, each with their
own drawbacks:
 
1) Run a single clustered volume group across all hosts, containing one
or more PV's from your shared storage.
 
2) Run a non-clustered volume group on each host, each with a distinct
PV carved out of your shared storage.
 
3) Export storage for each host individually from your SAN, i.e. rely
completely on your SAN for volume management.  With this you don't need
LVM at all.
 
Both 1) and 3) allow you to use Xen migration.  2) is feasible if you
don't need to migrate guests online.
 
Our problem with 1) is snapshot support, and that we could not get
pvmove to work acceptably well.  (We had to make the entire volume group
inactive before pvmove would even run--I'm not sure if it is expected,
or what we did wrong.)
 
We've tried and failed at 1), and will now be attempting 3).  This gives
us a lot of flexibility on a storage appliance that supports snapshots.
I'd still like to have pvmove work so we could migrate online from one
SAN to another, if needed, but I haven't been able to get it to work
acceptably well.
 
Also I thought I had read that snapshots are not supported by a
clustered LVM?  That would be difficult for us too, as we are relying on
snapshots for a backup mechanism.
 
Jeff


________________________________

	From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com] On Behalf Of Chris Edwards
	Sent: Friday, October 24, 2008 10:29 AM
	To: linux clustering
	Subject: RE: [Linux-cluster] Cluster and LVG/LV
	
	

	Yes to both.  Right now the cluster is running GFS and I can
migrate VM's between the nodes.   

	 

	This question is coming up because I have been trying to do a
snap shot and I realized the snapshot is stored on the Volume Group that
the LV is located on.  I did not realize  this and I cannot do a
snapshot because I did not leave enough space in each of the Volume
Groups for each of the VM's.

	 

	---

	 

	Chris Edwards
	Smartech Corp.
	Div. of AirNet Group

	http://www.airnetgroup.com <http://www.airnetgroup.com/> 

	http://www.smartechcorp.net <http://www.smartechcorp.net/> 

	cedwards at smartechcorp.net <mailto:agarrison at smartechcorp.net> 
	P:  423-664-7678 x114

	C:  423-593-6964

	F:  423-664-7680

	 

	From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com] On Behalf Of Jeff Sturm
	Sent: Friday, October 24, 2008 10:20 AM
	To: linux clustering
	Subject: RE: [Linux-cluster] Cluster and LVG/LV

	 

	Chris,

	 

	Are you running a clustered LVM, and do you expect to be able to
use Xen migration?

	 

	Jeff

		 

________________________________

		From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com] On Behalf Of Chris Edwards
		Sent: Friday, October 24, 2008 10:13 AM
		To: linux clustering
		Subject: [Linux-cluster] Cluster and LVG/LV

		If I am installing multiple Xen VM's in a cluster with
shared iSCSI space with Logical Volumes for each virtual machine should
I put each LV in its own logical volume group or should I use one
logical volume group for all of the LV's?

		 

		Thanks!

		 

		---

		 

		Chris Edwards

		 

		 

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