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VMware - VMDK file - Thick vs Thin Provisioning - Size/Compressed

  • 24 November 2023
  • 3 replies
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T
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Good morning,

I’m trying to wrap my head around the following case:

Let’s say there are two virtual machines, each with one 100 GB VMDK file (let’s ignore other files such as swap, etc. for the sake of this example). Each OS consumes 30 GB in total (Windows + Data).

  1. VM A - VMDK 100 GB, filled with 30 GB of data, thin provisioning
  1. VM B - VMDK 100 GB, filled with 30 GB of data, thick provisioning

The question is: will the full backup for VM A and VM B be of the same size (more or less) regardless the provisioning configured for each disk?

The idea behind this question is to know whether thin provisioning speeds up the backup process and consumes less storage at the end of the day (especially considering that we’re running out of backup storage).

Regards,

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Best answer by Chris Hollis 28 November 2023, 04:27

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Chris Hollis
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@Tommy 

The question is: will the full backup for VM A and VM B be of the same size (more or less) regardless the provisioning configured for each disk?

The answer is: yes, they’ll be roughly the same size regardless of how they are provisioned. 

Thick is just preallocated space, so you can’t overprovision. It’s not consuming the full 100GB so it’ll just be the size of the OS + Data at the time of backup.


Hopefully this helps!


Regards,​​​​​​​

Chris 

H
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Hello @Tommy 

Thin provisioning is more space efficient, as it only allocates the amount of data written, while thick provisioning allots the entire capacity. Having said that, I think performance-wise, thick provisioning is better as it eliminates the need to allocate space on demand. 

T
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Hi @Chris Hollis and @Hemanth 

Thanks for explaining this to me, I appreciate that 😉

I thought that since the size of the VMDK file was exactly the size provisioned, CV didn’t care about what was inside (nor about its structure) and just ‘copied' the entire (raw) file adding some compression or whatever.

@Hemanth - you’re absolutely right, however, there’s a fine document comparing both methods (thin vs thick); to make this long story short:

“The data we have collected reveals that VMware vStorage thin provisioning is at par in performance with the default method of provisioning in VMware (the usage of zeroes thick virtual disks).”

Also:

“ .. we determined that a workload run on a thin-provisoned disk performs very closely to that of a thick-provisioned disk, in both the zeroing and post-zeroing phases of disk growth.”

That is why I prefer thin provisioning over thick approach as it is much more flexible and almost as efficient.

If anyone would like to take a look at the document, I can share my copy as I don’t have the link to download it.

Regards,

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