> On 22 Mar 2021, at 14:27, Bryan Steele <bry...@gmail.com> wrote:
> 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
Makes a lot of sense. I guess a man page patch is in order.
Mischa
