Comments on: Provisioning KVM virtual machines on iSCSI with QNAP + virt-manager (Part 2 of 2)

By: Tim

Tim — Wed, 23 Mar 2011 00:33:41 +0000

Hi Daniel, Great tutorial. There are a couple of us having and issue with virt-manager and iscsi. I have added my issues to the bugzilla , I was just wondering if you had seen these issues with recent versions of libvirt/virt-manager

https://bugzilla.redhat.com/show_bug.cgi?id=669935

By: Matt

Matt — Tue, 24 Aug 2010 13:32:07 +0000

“Obviously care should be taken to not run the same VM on two machines at once though. Ideally use clustering software to protect against this scenario.” Have you found a good clustering solution for this? I have VM live migration with iSCSI working just great, but the ability to start a VM on multiple nodes is a big concern for production systems.

I had my eye on the Ovirt project, but it seems to have died down a bit.

By: Amadeus

Amadeus — Sun, 15 Aug 2010 05:42:15 +0000

Looking at /etc/rc3.d/

S02lvm2-monitor -> ../init.d/lvm2-monitor*

S07iscsid -> ../init.d/iscsid*

S13iscsi -> ../init.d/iscsi*

S97libvirtd -> ../init.d/libvirtd*

Could the problem be, that lvm2-monitor is started before iscsi?

By: Amadeus

Amadeus — Sun, 15 Aug 2010 05:28:00 +0000

If I don’t run “vgchange -ay vg00″ then I don’t get /dev/vg00. When I remote /dev/vg00 is gone. Can I add an LVM storage pool in virt-manager without the /dev/vg00 path?

I use:

localhost:~# rpm -qa|grep virt|sort

libvirt-0.6.3-33.el5_5.3

libvirt-python-0.6.3-33.el5_5.3

python-virtinst-0.400.3-9.el5

virt-manager-0.6.1-12.el5

virt-viewer-0.0.2-3.el5

localhost:~#

By: Daniel Berrange

Daniel Berrange — Sun, 15 Aug 2010 02:09:45 +0000

That shouldn’t be required subsequently, since libvirt automatically runs ‘vgchange -ay $NAME’ when it starts a LVM storage pool. In fact it shouldn’t really have been required in the first instance either. libvirt has a method to discover valid storage pool sources and thus in theory virt-manager should have been able to present you with a list of LVM pool names automatically.

By: Amadeus

Amadeus — Sun, 15 Aug 2010 01:52:47 +0000

Okay, I sort of found out the solution =)

vgchange -ay vg00

gives me /dev/vg00

But it doesn’t happen by it self after reboot, and suspect it should happen quite early in the boot sequence, so adding it to rc.local wouldn’t probably be early enough for libvirt?

What would you do in this situation?

By: Amadeus

Amadeus — Sun, 15 Aug 2010 01:40:04 +0000

Okay, now I have connected a target with 1 LUN which contains an LVM partition, which contains a Volume Group (called vg00)with 1 Logical Volume.

Now I would like to add this LVM partition to libvirt’s storage pool, so I select LVM in your “Adding a storage pool”.

Then I have to enter a path for the Volume Group.

The problem is that I don’t see /dev/vg00 as I would expect. I have a local LVM partition called “vol” and I can add that by /dev/vol to libvirt, and it works perfectly in virt-manager.

The path for vg00 is

/dev/disk/by-path/ip-192.168.0.4:3260-iscsi-iqn.2004-04.com.qnap:ts-509:iscsi.linux02.ba4731-lun-0-part1

But I can’t enter that. virt-manager file chooser wants a directory, not a file.

Do you know how to add this Volume Group as a storage pool?

By: Amadeus

Amadeus — Tue, 10 Aug 2010 12:01:05 +0000

Excellent. Thanks a lot!

By: Daniel Berrange

Daniel Berrange — Tue, 10 Aug 2010 02:37:31 +0000

If you have multiple hosts and want different LUNs visible on each host, then you might want multiple targets – each host would login to a different target, thus seeing different LUNs. If you want all your hosts to always see the same LUNs, then 1 target with multiple LUNs would work just fine. Personally I just use one target, many LUNs.

By: Amadeus

Amadeus — Tue, 10 Aug 2010 00:36:01 +0000

Ok, now I am ready to deploy your howto.

I have 1 QNAP and 3 KVM hosts. I will give each KVM host a LUN with LVM inside.

Are you aware of pros and cons in using “1 target + 3 LUNs” or “3 targets + 3 LUNs”?

What would you recommend?