Seeking advice on virtualization

Tomasz Rola rtomek at
Tue Aug 7 17:07:06 UTC 2018

On Mon, Aug 06, 2018 at 12:07:13AM +0100, Paul Webster wrote:
> In theory as ZFS works on both linux and BSD you could simply use vdevs and
> snapshots for easy transport


I was writing about "hard disk file" format, in which a hypervisor
(i.e. bhyve, kvm, virtualbox) is keeping a disk for emulated
machine. Wikipedia calls it "img format":

Advantage from using this format (as opposed to something like qcow or
vmhd) is that, in theory (and even in practice) one can boot such
machine (I mean, virtual machine defined with such "raw" hard drives)
using any hypervisor. Or to put it differently, it is not proprietary
and is the easiest one to implement, so it is what most probably will
keep being used years or decades from now (in whatever hypervisor / PC
emulator of the future day is fashionable).

I believe in the past I have installed an OS (say, FreeDOS) using
virtualbox and after deciding I would not use virtualbox in a future,
I started to boot said machine using kvm. Likewise, I believe some
OSes rejected being installed under certain hypervisor, so one had to
install them using this other hypervisor and then could happily
continue to run it under his preferred hypervisor.

All of this made possible thanks to avoiding file formats supported by
one or only few hypervisors.

Of course there are many hd-file formats and some are supported by
more than one hypervisor, but the easiest one is raw and in case of
emergency it can be also mounted as any other block device (always, I
guess, but I would pay attention to block size mismatch).

Tomasz Rola

** A C programmer asked whether computer had Buddha's nature.      **
** As the answer, master did "rm -rif" on the programmer's home    **
** directory. And then the C programmer became enlightened...      **
**                                                                 **
** Tomasz Rola          mailto:tomasz_rola at             **

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