(this is similar to my How to tell virsh: save state of VM and vdisk, but not attached disk? but for VirtualBox and raw devices)
How do I tell VirtualBox to NOT preserve the state of raw attached devices when snapshotting? Details:
- I created a VMDK on the host machine as follows:
VBoxManage internalcommands createrawvmdk -filename sdb.vmdk -rawdisk /dev/sdb
and attached it to the guest.
/dev/sdb now shows up as a pure device file on the guest.
My clever idea: mount /dev/sdb, and any changes I make there will be preserved across snapshots, since VirtualBox isn't going to save the state of /dev/sdb
I was wrong. By default, VirtualBox will save the state of /dev/sdb: if you revert to an earlier snapshot, anything you did on /dev/sdb will be wiped out.
In other words, my cunning plan failed.
Is there any way to make it work? I realize I could mount /dev/sdb on the host and then have the guest mount it or sshfs it or something, but is there a VirtualBox option that says "do not preserve/restore /dev/sdb state when snapshotting"?
I'm trying to use a VM to determine how I want to install CentOS 7.2, and, ideally, I'd like the guest to be as close to a real system as possible.
I'd like to thank @gilles for his excellent answer, but it turns out that it doesn't quite work.
When I shutdown, detach /dev/sdb, take a snapshot and then later restore the snapshot and re-attach /dev/sdb, I see this (click for full size):
Basically, VirtualBox refuses to touch /dev/sdb, even if I attach it. Rather, it uses differencing disks to store any changes I make, and these changes are reverted when I restore snapshots.
You can actually see the differencing disks in Media Manager:
but I can't find a way to do anything useful with them.
I'm leaving my upvote and checkmark for gilles answer, but will go back to using more normal methods to mount /dev/sdb on the guest.
