[URGENT] Is 'virt-install' cannot generate isolated VMs using same existing qcow2 ?

donghyun Kim · 10-02-2014, 09:38 AM

Hello,

I have a big trouble on using kvm-libvirt.

I have a customized qcow2 image (I extracted it using virtualbox-NAT network)

and generated 3 VMs.

Each customized VM download network interface file from remote server in booting process onto its mac address and automatically change its /etc/network/interfaces.

when I generate 1 VM, it works well, but 3 VMs work wrong. I think that multiple VMs share each resource and network configuration process goes wrong. When I install new VM machine using same qcow2, after that the network setting is not same with default qcow2 network setting (I think that My networking change process is reflected on it)

My VM installation ex command is as below (VMs: test1,test2,test3)

virt-insatll --name test2 --ram 512 --vcpus 1 --disk path=/home/dhkim/image/1002_ver6.qcow2,format=qcow2,sparse=true --noautoconsole --import --force --mac 08:00:27:re:5d:12

How can I generate multiple isolated VMs without changing original qcow2 image in command?
(I want to get same result - for example virtualbox, <new> VM, not import, and bring *.vmdk existing image and start, repeat 3 times , and then generate 3 isolated VMs)

please reply me,

Thank you

Habitual · 10-02-2014, 09:51 AM

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you using the same mac address for all 3?

donghyun Kim · 10-02-2014, 12:23 PM

of course not I used diffrent mac address

dyasny · 10-03-2014, 08:38 AM

did you use the same qcow2 file for all three VMs, or did you clone the file/take three different snapshot of the original template?

did you wipe /etc/udev/rules.d/70-persistent-net.rules before cloning the VM image?

donghyun Kim · 10-03-2014, 11:28 PM

Quote:

Originally Posted by dyasny

did you use the same qcow2 file for all three VMs, or did you clone the file/take three different snapshot of the original template?

did you wipe /etc/udev/rules.d/70-persistent-net.rules before cloning the VM image?

--> Oh I used same qcow2 image and import it all 3 VMs, How can I clone snapshot qcow2? and Do I have to wipe 70-persistent-net.rules in host? guest? and could you please explain why?

Slax-Dude · 10-04-2014, 09:25 AM

First, wipe 70-persistent-net.rules on the qcow2 image.
Second, create snapshots for each VM.

You are trying to use the same qcow2 image for 3 different VMs, and that is the equivalent to using 3 computers with the same hard drive... it simply can not be done.

Using a snapshot, however, you can use your original qcow2 image as a read-only gold image and the snapshot is where files are written.

See documentation: http://wiki.qemu.org/Documentation/CreateSnapshot

dyasny · 10-04-2014, 07:30 PM

you cannot attach 3 VMs to the same disk image. Imagine connecting one hard drive to three separate computers as the main and only drive. You need to either make 3 copies of the original qcow2 or use qemu-img to create three snapshots and base your VMs on those. The latter option will save you some space (though it might end up being more space wasted in the long run) but it will cost you some disk access speed.

the persistent-net.rules file should be wiped in the guests. Don't know about Ubuntu, but in RHEL there's a "sys-unconfig" utility which will prepare the system to be redeployed, essentially removing ssh keys, mac address references and other individual host settings, so the image can be easily cloned.

donghyun Kim · 10-05-2014, 12:58 AM

Quote:

Originally Posted by dyasny

you cannot attach 3 VMs to the same disk image. Imagine connecting one hard drive to three separate computers as the main and only drive. You need to either make 3 copies of the original qcow2 or use qemu-img to create three snapshots and base your VMs on those. The latter option will save you some space (though it might end up being more space wasted in the long run) but it will cost you some disk access speed.

the persistent-net.rules file should be wiped in the guests. Don't know about Ubuntu, but in RHEL there's a "sys-unconfig" utility which will prepare the system to be redeployed, essentially removing ssh keys, mac address references and other individual host settings, so the image can be easily cloned.

In Openstack, I can generate multiple VMs using single qcow2 image easily without copying the image. I don't know exactly how it is going on, Is there any option to generate multiple VMs using libvirt like openstack?

dyasny · 10-05-2014, 12:51 PM

Quote:

Originally Posted by donghyun Kim

In Openstack, I can generate multiple VMs using single qcow2 image easily without copying the image. I don't know exactly how it is going on, Is there any option to generate multiple VMs using libvirt like openstack?

openstack (well, nova actually) will copy a disk copy for every instance from the glance image repository. So on the host that runs the VMs, you get three disk image copies.