[Linux-cluster] Cluster and LVG/LV

[Chris Edwards]

Thanks for the advice!

So could I use vgmerge to merge all of my volume groups into one large volume group then?

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Chris Edwards


From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Rodrique Heron
Sent: Friday, October 24, 2008 11:55 AM
To: linux clustering
Subject: RE: [Linux-cluster] Cluster and LVG/LV

Jeff-

Thanks for your thoughts, until now I never really considered exporting storage from the SAN to my domU's. I can definitely see the advantage here, using the SAN snapshot utilities, it most cases it can be automated. I am interested in how you would accomplish similar functionality to the SAN snapshot, using LVM snapshots (let's say lvm snapshot support worked well).

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From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Jeff Sturm
Sent: Friday, October 24, 2008 11:00 AM
To: linux clustering
Subject: RE: [Linux-cluster] Cluster and LVG/LV

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

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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.

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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!

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Chris Edwards


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