Arch Linux

alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

qemu-kvm: default devices and qcow2 overlays

I'm considering migrating a critical VM from VBox to qemu-kvm.  I've already played around with qemu a bit, but I have two questions I can't find answers to.

The first is about the default devices that are 'created' when using a basic qemu command (such as qemu <qemu_image>).  I'd like to find out exactly what would be the commands to create those devices to help me create an optimal VM for my needs.  But I can't find any information about what's created, much less how it would be created manually.  The qemu monitor command info <subcommand> doesn't help much here, not least because I can't figure out how to page the output or send it to a file.

Second, I have several VMs which have three or more discrete 'states' as far as the contents of the virtual HDD.  IOW, I install the OS, shutdown, and take a snapshot.  Then I install some s/w, shutdown, and take another ss.  Then I revert to the first ss, install some other s/w, shutdown, and take a third ss.  Rinse, repeat.  I'm only interested in the contents of the virtual HDD, 'differencing images' in VBox terms I think.  The hardware config does not change, and I take snapshots when shutdown, so I'm not looking to duplicate h/w config save or 'state save' features of VBox snapshots.  Are qcow2 and the associated 'overlays' the right tool for this job?

Thanks.

Last edited by alphaniner (2012-12-13 19:52:25)

---

But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner