Seeking advice on virtualization

[Jakub Chromy]

> even cooler you get 'clones' so you can say make a raw/zvol of debian 
> or whatever you like then if you make a snapshot of it and clone it to 
> something else 'debian2' it uses no space until you write/delete/edit 
> something, basically the clone only has diffs.

yep... but it has some downsides too.. try to delete the original 
(source) ZVOL. Impossible until you remove the daughter clones first.

> And yes zvols are literally like raw devices, dd style you can infact 
> take a raw image and dd it to a zvol

yes... and you can even create sparse volumes (-s flag).. supercool :)


>
> On 7 August 2018 at 19:57, Jakub Chromy <hicks at cgi.cz 
> <mailto:hicks at cgi.cz>> wrote:
>
>         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":
>
>         https://en.wikipedia.org/wiki/IMG_(file_format)
>         <https://en.wikipedia.org/wiki/IMG_%28file_format%29>
>
>         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.
>
>
>     ZFS ZVOL is a true "raw device" as well... (or at least it did
>     behave like that for me):
>
>       dd if=/dev/zvol/pool/mypornhubpremiumarchive0
>     of=/var/vm/mypornhubpremiumarchive0.raw
>
>     but you get snapshots, zfs send | zfs recv and stuff.
>
>     -- 
>
>
>        regards / s pozdravem
>
>
>     Jakub Chromy
>
>
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>
>     On 7.8.2018 19:06, Tomasz Rola wrote:
>
>         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
>
>         Um-hm.
>
>         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":
>
>         https://en.wikipedia.org/wiki/IMG_(file_format)
>         <https://en.wikipedia.org/wiki/IMG_%28file_format%29>
>
>         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).
>
>
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