How much space does a Virtual Machine Consume?

[gavinmansell]

I have read that there is a generic formula for calculating the space that a VM will consume on a LUN.... VM Hard disk file + VM suspended state + memory reservation = Minimum storage requirement for a VM.

Is this an accurate formula to use? If so, I am a little worried as we have a number of LUNs (approximately 500GB in size) with less than 20% free space and have not been using this formula to calculate space

For example if we had 5 VMs with 50GB VMDK file and a 2GB memory reservation that would total 260GB... Using the formula, there would be another 250GB required for the VMs suspended states. This would take the amount of space requied above the amount of space available on the LUN.

Is this formula a best practice or something that is a nice to have? I can see it making storage a lot more expensive!

[avlieshout]

In general for 90% a vm's size is calculated by summarizing the vm's virtual disk files and the vm's swap file (limit-reservation)

You need some extra space for creating snapshots. I always leav 10% free space for creating snapshots, but snapshots are managed very tightly and are only allowed for a maximum of 1 week. To have more breathing space you could leave 20% free space, which is a more common practice.

I wouldn't calculate the suspend state for each vm, since I don't suspend or snapshot all vms at the same time.

To know the total size of your vm, I recently created a Powershell script for that. see

-Arnim van Lieshout

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[azn2kew]

Here is a great LUN sizing formula from Edward Haletky when you planning storage requirements:

Conservative sizing: assuming size of VM static which it is not usually but you get the idea.

Size of VM = Size of VMDK + SIze of VMDK (for full snapshot) + Size of Memory + 15MBs + 4GB (logs)

Size of LUN = Size of VM * # of VMs * 1.2

Always leave yourself 20% free space on the LUN in case of emergency and other issues.

If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!

Regards,

Stefan Nguyen

VMware vExpert 2009

iGeek Systems Inc.

VMware, Citrix, Microsoft Consultant

[AndreTheGiant]

The swap area of a VM is the Total vRAM minus the memory reservation.

You will also need some space for log (very little) and for snapshot (vary variable, if you forget to remove).

And the space could change again if you use thin disks.

IMHO is better use a statistical approach and monitor the free space on datastore

Andre