Idea: immutable base-disk images and per-VM differencing images

[Mike Williams]

Before discovering Vagrant, I had my own script to create VirtualBox VMs.  While it was in most ways vastly inferior to Vagrant, I did manage to speed up creation of new VMs, by sharing the base disk image.

• I marked my base disk image as "immutable"
• I attached the base disk image directly to new VMs, rather than making a copy first.  Being "immutable", VirtualBox creates a new copy-on-write "differencing image" for the VM.
• Finally, I disabled "auto-reset" the new "differencing image".  When VirtualBox creates a "differencing" child of an immutable image, the default behaviour is to discard changes whenever the VM starts.  That's most definitely not what I wanted.

It seems to me like this would be a useful addition to Vagrant, and in fact, could/should be the default behaviour.  Imported box images would be marked immutable, and it would create a new "differencing" child image for each new VM.

Can anyone see any downsides to this approach?  If not, I'll have a crack at implementing it.

-- 

cheers, 

Mike Williams

[Blake]

I learn something new every day. This sounds like a great idea, and
would save tons of space, not just time to creation.

Blake

On Friday, October 22, 2010, Mike Williams <md...@dogbiscuit.org> wrote:
> Before discovering Vagrant, I had my own script to create VirtualBox VMs.  While it was in most ways vastly inferior to Vagrant, I did manage to speed up creation of new VMs, by sharing the base disk image.

> I marked my base disk image as "immutable"I attached the base disk image directly to new VMs, rather than making a copy first.  Being "immutable", VirtualBox creates a new copy-on-write "differencing image" for the VM.Finally, I disabled "auto-reset" the new "differencing image".  When VirtualBox creates a "differencing" child of an immutable image, the default behaviour is to discard changes whenever the VM starts.  That's most definitely not what I wanted.

[Raja]

On Oct 22, 4:24 pm, Mike Williams <m...@dogbiscuit.org> wrote:
> Before discovering Vagrant, I had my own script to create VirtualBox VMs.  While it was in most ways vastly inferior to Vagrant, I did manage to speed up creation of new VMs, by sharing the base disk image.
>
> I marked my base disk image as "immutable"
> I attached the base disk image directly to new VMs, rather than making a copy first.  Being "immutable", VirtualBox creates a new copy-on-write "differencing image" for the VM.
> Finally, I disabled "auto-reset" the new "differencing image".  When VirtualBox creates a "differencing" child of an immutable image, the default behaviour is to discard changes whenever the VM starts.  That's most definitely not what I wanted.

This is interesting, can you explain how this is done? Everytime you
start up the VM, how would you provide the "differences" that were
done after the VM was created.

Thanks
Raja

[Blake]

Raja,
If this is indeed a copy-on-write method, then any changed blocks
would be stored in a separate file for that VM. Unchanged blocks
would remain in the original/master VM image.

Blake

[Mike Williams]

On 23/10/2010, at 04:30 , Blake wrote:

> Raja,
> If this is indeed a copy-on-write method, then any changed blocks
> would be stored in a separate file for that VM. Unchanged blocks
> would remain in the original/master VM image.

Precisely.

See http://www.virtualbox.org/manual/ch05.html#diffimages for details.

--
cheers,
Mike Williams

[CjK]

Well I assume that one definite drawback will be reduced performance.
As "copy-on-write" implies, there will be increased disk-activity.

Claus

[Sami Samhuri]

On Oct 25, 12:37 am, CjK <claus.klingb...@gmail.com> wrote:
> Well I assume that one definite drawback will be reduced performance.
> As "copy-on-write" implies, there will be increased disk-activity.

How so? Things are written to a location different from where they
were read but the same amount of data should be written.

Seeks may increase switching between the 2 files but large disk images
are going to get fragmented anyway.

-s

[Mitchell Hashimoto]

Mike,

Sorry it took so long to respond. This email was sent when I was out
of town and I completely forgot about it until now. This is definitely
something I will have to look into and that I'm very interested in
doing. I'll keep you up to date on what the status of this is. I don't
see any downsides to it if it works just as you described. I wasn't
even aware of this functionality!

Mitchell

[Edward Evans]

Was this ever implemented and if so can you point me to any details?
Tia

[Torben Knerr]

Yes, see the linked clones section here:
https://www.vagrantup.com/docs/virtualbox/configuration.html

HTH, Torben

Am 13.08.2016 8:11 nachm. schrieb "Edward Evans" <ed.e...@gmail.com>:

Was this ever implemented and if so can you point me to any details?
Tia

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[Edward Evans]

Yes, indeed. Thanks so much!

[Edward Evans]

Actually, I was hoping for something more like this that is for HyperV being enabled for VB.  As I understand it, the linked clones only works for multi-machine.  Am I wrong here?

https://github.com/mitchellh/vagrant/pull/7090

On Saturday, August 13, 2016 at 3:18:10 PM UTC-5, Torben Knerr wrote:

Yes, see the linked clones section here:
https://www.vagrantup.com/docs/virtualbox/configuration.html

HTH, Torben

Am 13.08.2016 8:11 nachm. schrieb "Edward Evans" <ed.e...@gmail.com>:

Was this ever implemented and if so can you point me to any details?
Tia

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[Alvaro Miranda Aguilera]

not necesarily for multi machine

my understanding is on the 2nd and so on guest from the same template

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[Edward Evans]

Right, but with the HyperV support, the first box uses a diff disk whereas with with the VB and linked clones only 2nd and successive use diff disk, right?

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Alvaro

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[Alvaro Miranda Aguilera]

what i understand, is with virtuabox this is what it does.

base box -> base full clone for linked clones

base -> linked clone1

base -> linked clone2

that is to ensure the linked clone are independent from the base box, since vagrant box remove <name> wont check for linked clones of base boxes.

Thats from memory from when the feature was implemented.

It should be with comments on the source code

Alvaro.

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Alvaro

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