On Mon, Mar 22, 2021 at 01:47:18PM +0100, Mischa wrote:
>
>
> > On 22 Mar 2021, at 13:43, Stuart Henderson <s...@spacehopper.org> wrote:
> >
> >>> Created a fresh install qcow2 image and derived 35 new VMs from it.
> >>> Then I started all the VMs in four cycles, 10 VMs per cycle and waiting
> >>> 240 seconds after each cycle.
> >>> Similar to the staggered start based on the amount of CPUs.
> >
> >> For me this is not enough info to even try to reproduce, I know little
> >> of vmm or vmd and have no idea what "derive" means in this context.
> >
> > This is a big bit of information that was missing from the original
>
> Well.. could have been better described indeed. :))
> " I created 41 additional VMs based on a single qcow2 base image.”
>
> > report ;) qcow has a concept of a read-only base image (or 'backing
> > file') which can be shared between VMs, with writes diverted to a
> > separate image ('derived image').
> >
> > So e.g. you can create a base image, do a simple OS install for a
> > particular OS version to that base image, then you stop using that
> > for a VM and just use it as a base to create derived images from.
> > You then run VMs using the derived image and make whatever config
> > changes. If you have a bunch of VMs using the same OS release then
> > you save some disk space for the common files.
> >
> > Mischa did you leave a VM running which is working on the base
> > image directly? That would certainly cause problems.
>
> I did indeed. Let me try that again without keeping the base image running.
>
> Mischa
I seemed to recall that the base image is not supposed to be modified,
so this is a pretty big omission.
Per original commit message:
"A limitation of this format is that modifying the base image will
corrupt the derived image."
https://marc.info/?l=openbsd-cvs&m=153901633011716&w=2
-Bryan.
