View Full Version : I want use VMM with LVM and qcow2, but it doesn't work

03-Feb-2015, 19:31
Hello Forum Users,

my Problem is about Virtual Machine Manager and the Storage configuration in a SLES12 environment with KVM/qemu.

I want use the VMM with LVM and the qcow2 format.

My first config is:

A LVM Group with a new volume. If I use this I can use any GB space for the Virtual Machine
I want. But I cannot use the qcow2 format.

My second config is:

I use a ( in German: ) „Dateisystemverzeichnis“ my data space cannot be bigger then 8 GB. But I can use the qcow2 format.

In two scenarios both cases are work.
First: I use the default directory from VMM, or I use a Folder in my /home directory.

My wish is two use my second Hard Disk with many Logical Volumes for many Virtual Machines.

Thank you for read,

04-Feb-2015, 17:52
Hi Flo,

while I cannot give any help with the actual question (haven't used neither SLES12 nor KVM), your last statement triggered a warning:

> My wish is two use my second Hard Disk with many Logical Volumes for many Virtual Machines.

Many virtual machines on a single hard disk will cause many iowaits ;) At least if you run more than a few VMs concurrently.

Back on topic:

> But I cannot use the qcow2 format.

So that others can get a better picture of the situation: *why* can't you use it? Do you receive an error message, are you using some tool that will not offer an according selection? Since (from what I can tell) using QCOW2 on top of logical volumes should be technically possible, some more details might be helpful.


05-Feb-2015, 18:56
Hi Jens,

Thank you for your reply.

Your first reply isn't for my use case. I don't want to run the Virtual Machines on the same time.
Rather for learning various types of server applications not on the same time.

I don't use any other tool that can generate an error.

The first config:

If I use LVM in the Menu for create a StorageVolume I have no choice to use qcow2.
And when I choose the same (qcow2) in the last Config Menu again (there is a summary of all points again) I get following error message:

„Installation konnte nicht fertiggestellt werden: <<internal error: exited while connecting to monitor: 2015-02-05T15:46:49.677413Z qemu-system-x86_64: -drive file=/dev/vgDATE/testdate001,if=none,id=drive-virtio-disk0,format=qcow2,cache=unsafe,aio=native:could not open disk image /dev/vgDATE/testdate001:
Image is not in qcow2 format>>

Traceback (most recent call last):
File „/usr/share/virt-manager/virtManager/asyncjob.py“, line 91, in cb_wrapper

callback(asyncjob, *args, **kwargs)
File „/usr/share/virt-manager/virtManager/create.py“, line 1908, in do_install
File „/usr/share/virt-manager/virtinst/guest.py“, line 426, in start_install noboot)
File „/usr/share/virt-manager/virtinst/guest.py“, line 490, in create guest
dom = self.conn.createLinux (start_xml or final_xml, 0)
File „/usr/lib64/python2.7/site-packages/libvirt.py“, line 3297, in createLiinux
if ret is None:raise libvirtError('virDomainCreateLinux() failed',conn=self)

The second config:

If I use (In German:) „Dateisystemverzeichnis“ in the Menu for create a StorageVolume I have the choice: qcow2. There is no error message but in the menu I can't change the Volume size. And I can not set over 7.75 GB.

Maybe I have a chance to do all this in the command line but I have little hope.

Thanks for all,

06-Feb-2015, 13:26
Hi Flo,

if I read this correctly, then you're talking about virtmanager on the host. Oh, and I'm not too familiar with the GUI tools, I usually work with the command line and/or automation tools to generate configs ;)

QCOW2 is a "format" - so you need to "format" the logical volume in the QCOW2 format. I haven't toyed with that yet, but it's worth a try to apply the qemu command right on the LV, instead of a file inside the LV.

What your second approach tries to do in the background, I can only guess: it probably will create a file in the QCOW2 format. Not permitting you to change the volume size (the size of the underlying volume/file system) is expected - from the front end view, the file system is a given and would need to be changed in advance by the admin. That you cannot set a file size above 7.75 GB may be a limit of the file system, is there enough free space? The QCOW2 format will support larger files, it has a 64bit integer representing the image file size.


06-Feb-2015, 18:46
Hello Jens, thanks for reply,

in the last hours I approximate my search to the command line tool like virsh (a tool for Virtual Machines). I see there are more possibilities. I must read a lot about the topic before I can make a new statement.

Thank you very much,