Unable to boot into offline Ubuntu guest snapshot on Ubuntu host

[aWak3N]

Hello,

I am unable to boot from a clean shut down (=offline) Virtualbox snapshot since yesterday. The sceen simply remains black after going through BIOS. Booting from online snapshots works flawlessly. Booting from older offline snapshots does also work. If I have VT-x enabled, I get no error or progress message at all. Disabling VT-x shows the Guru Meditation message saying a critical error had occured.

Thank you!

[aWak3N]

Booting from an offline snapshot without VT-x

[aWak3N]

Screenshot black screen

[aWak3N]

Additionally it is not even possible to just normally _reboot_ my host system. It always gets stuck after the BIOS. Help please!

[Frank Mehnert]

Are your virtual disk images located on an ext4 drive?

[aWak3N]

Yes, they are indeed located on an ext4 drive as this is the default filesystem of my Ubuntu 10.04 host installation. I, however, have no problems booting "older" offline snapshots which are also located on this ext4 partition. Could it be a problem introduced by an updated Virtualbox version?

[Frank Mehnert]

Yes, probably. There is an ​ext4 bug which is triggered by the way how VirtualBox 3.2.x is accessing virtual disk images. Starting with VBox 3.2.x, host disk caching is disabled for virtual disk images attached to a SATA or SCSI controller. The work around is to enable this cache in the VM settings or to put the files on an ext3 partition. Unfortunately we were not aware of the bug at the time we released VirtualBox 3.2.4.

[aWak3N]

I enabled Host disk caching in the options, but it didnt affect the erroneous behaviour: I'm still unable to boot off an offline image or simple reboot my vm. Unfortunately I can't test the vdi file on an ext3 partition. I am pretty positive this bug was not present on the previous version of VBox 3.2.x (I think it was 3.2.3).

[Frank Mehnert]

I fear your snapshot is already corrupted by this bug, therefore you have probably remove this snapshot.

[aWak3N]

I tried it with an older offline snapshot (which was not corrupted) and enabled host disk caching and i could reboot that system without a problem. I guess the filesystem might get corrupted upon shutdown, that's why i've been having no problem resuming online snapshots. Is it somehow possible to activate host disk caching on a runnning vm, because otherwise i would lose a lot of work and data...

[Frank Mehnert]

Enabling the host cache wouldn't solve your problem as the data in the snapshot is most probably already corrupted.

[aWak3N]

Ok i backed up all my files and reverted to a working snapshot. One last question: Is activating disk host caching affecting a system's performance?

[Frank Mehnert]

I believe you will not note a difference, only under certain circumstances. Note that VBox 3.2.6 will show a warning and will automatically enable the host cache if the disk image is located on an ext4 partition.