[Qemu-devel] Using the one disk image file on 2 virtual machines at the same time

[한만종]

Hi,

I'm facing a weird behavior when I used the one disk image file on 2 virtual machines at the same time.

I made the instance of a virtual machine, using the below command.

$ qemu-system-x86_64 -smp 2 -m 1024 -hda 10G.qcow2 -enable-kvm

When the OS(Ubuntu 14.04 64bit) was booted up, I made an another one, using the same command.

$ qemu-system-x86_64 -smp 2 -m 1024 -hda 10G.qcow2 -enable-kvm

Then, I had 2 virtual machines using the same disk image file.

When I made a directory on first virtual machine, using the command like below.

$ mkdir test1

The "test1" directory wasn't showed on another virtual machine. And, I made a directory on second virtual machine, using the command like below.

$ mkdir test2

The "test2" directory wasn't showed on another virtual machine, either.

Then, I shut the all virtual machines down. I tried to mount the disk image file on my host machine.

$ sudo modprobe nbd

$ sudo qemu-nbd -c /dev/nbd0 ./10G.qcow2

$ sudo mount /dev/nbd0p1 /mnt/10G

Then, I checked what the file is showed. The result was that "test2" directory was only showed.

Where is the "test1" directory? This is the weird behavior on my test.

Before my test, I created a disk image file and installed the OS on the disk image, using the commands like below.

$ qemu-img create -f qcow2 -o preallocation=metadata 10G.qcow2 10G

$ qemu-system-x86_64 -smp 2 -m 2048 -hda 10G.qcow2 -cdrom ../iso/ubuntu-1404.2-desktop-x86_64.iso -enable-kvm