virtual machines get damaged in a MultiAttach context

[Arbiel Perlacremaz]

Hi

I first wrongly reported this bug under OpenStack, due to a misunderstanding of the bug reporting procedure. It received there # 1657726.

I'm running VirtualBox Version 4.3.12 r93733.

The Windows application I run accesses a single file, and is not able to handle concurrently the two files I have to manage. So I decided to create two VirtualBox virtual machines, one for each file. To be able to run the two virtual machines concurrently when I need access to both
files, and to save disk space, I decided to use the multiattach option, as it fits my needs.

In this context, the last virtual machine to be closed gets damaged after closure : hard disks description in the vbox file are removed.

Instead of reading

      <HardDisks>
        <HardDisk uuid="{7cb32070-cfe6-42ae-8ceb-243dc99f82d8}" location="/home/comptes/Fichiers Money/Comptes_VBO_VM/Comptes (vdi)" format="VDI" type="MultiAttach">
          <HardDisk uuid="{1e94c103-618d-4567-b5e4-81865aef6c3c}" location="Snapshots/{1e94c103-618d-4567-b5e4-81865aef6c3c}.vdi" format="VDI"/>
        </HardDisk>
      </HardDisks>

hard disk description gets

      <HardDisks/>

The same damage keeps occurring until next reboot even if the relaunched machine remains the only running machine.

I consider this to be a bug as section "5.4 Special image write modes" of the "Oracle
VM VitualBox® User Manual version 5.1.14"
(https://www.virtualbox.org/manual/UserManual.html) reads as follows

§5 An image in multiattach mode can be attached to more than one virtual
machine at the same time, even if these machines are running
simultaneously. For each virtual machine to which such an image is
attached, a differencing image is created. As a result, data that is
written to such a virtual disk by one machine is not seen by the other
machines to which the image is attached; each machine creates its own
write history of the multiattach image.

As long I'm concerned, I wrote a script to bypass this issue, so that there is no hurry for me for this issue to be fixed. However, other users may be in great difficulty to use the multiattach option.

Arbiel