Convert Dynamic to fixed-size virtualdisk

Discussions related to using VirtualBox on Linux hosts.

Re: Convert Dynamic to fixed-size virtualdisk

Postby bulblight » 30. Aug 2016, 04:50

I don't know why the upgrade to Ubuntu 16.04 complained that there was no free disk space on the virtual dynamic drive but when I converted it to fixed it did not complain and continued with the install??
The upgrade reported the free disk space remaining as though the virtual amount was a fixed disk.
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Re: Convert Dynamic to fixed-size virtualdisk

Postby mpack » 30. Aug 2016, 09:56

I can't comment on what you think you saw, I can only tell you that what you reported was not possible, for the reasons given.

To prove me wrong, just show any evidence at all that a guest is somehow aware of the host VDI file size - and don't confuse space used with host file size: space used would be the same if the drive was fixed size. Another difference is that space used goes down when files inside the guest are deleted, but the host VDI file does not shrink.
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Re: Convert Dynamic to fixed-size virtualdisk

Postby Finlay15 » 8. Nov 2016, 20:54

With regards to the 2nd post in this thread - a very odd statement since it's practically the first sentence in the manual regarding dynamic disks.

For more flexible storage management, use a dynamically allocated image. This will initially be very small and not occupy any space for unused virtual disk sectors, but will grow every time a disk sector is written to for the first time, until the drive reaches the maximum capacity chosen when the drive was created. While this format takes less space initially, the fact that VirtualBox needs to expand the image file consumes additional computing resources, so until the disk file size has stabilized, write operations may be slower than with fixed size disks.

It's not as if the concept came out of thin air.
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Re: Convert Dynamic to fixed-size virtualdisk

Postby socratis » 8. Nov 2016, 21:21

Finlay15 wrote:the fact that VirtualBox needs to expand the image file consumes additional computing resources, so until the disk file size has stabilized, write operations may be slower than with fixed size disks.

The statement that you're trying to say didn't make sense, is that fixed disks are faster than dynamic disks. That is true and does in fact make sense. Imagine, as a simplistic example, that you have some uneven, rough terrain that you have to bike through.
  • In the fixed case, a bulldozer flattens the whole thing before you start taking the ride. That takes a lot of initial time, as you have to wait for the bulldozer to be done with the whole area, before you even mount your bike.
  • In the dynamic case, the bulldozer is in front of your bike and flattens the terrain as you go. Just not as slow of a bulldozer, and you can still take rides in the already flattened area.
  • Once your total biking area is flattened, the bulldozer is out of the way for good and you can bike at the same speed. And frankly you don't care at that point if there was ever a bulldozer to begin with.
Hope you can visualize it better.
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Re: Convert Dynamic to fixed-size virtualdisk

Postby mpack » 8. Nov 2016, 23:17

Finlay15 wrote:With regards to the 2nd post in this thread - a very odd statement since it's practically the first sentence in the manual regarding dynamic disks. [...]

Since I wrote both the second post in this topic, and that paragraph in the user manual, I can assure you that there is no contradiction. I can't help it if you refuse to set aside your preconception of what either should say.
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