vCloud Director thin provisioning & storage allocation per allocation model

I have run into several discussions lately regarding the thin provisioning option, storage over subscription and the storage allocation per Organization virtual datacenter (Org vDC) in vCloud Director (vCD).

This is my way of clarifying what to expect from the different options and rule out potential missunderstandings.

You activate the thin provisioning option when you initially create the Org vDC.

By default thin provisioning is not enabled, fast provisioning is enabled.

You can change (enable/disable) the thin provisioning option when the Org vDC is created by right clicking on the Org vDC, select Properties and select Storage tab:

The amount of storage allocated to an Org vDC is configured when creating the Org vDC. You can change the amount of storage allocated to an Org vDC by going to the “Storage Profiles” tab, select “Properties” of the “Storage Profile” you want to manage and set the storage limit.
Type X GB or select Unlimited, for the allocation model “Pay-As-You-Go” or type X GB for allocation models “Allocation Pool” and “Reservation Pool”. 

Below figure shows the configuration options for allocation model “Pay-As-You-Go”.
Below figure shows the configuration option for allocation models “Allocation Pool” and “Reservation Pool”.

Now we have covered how to manage (enable/disable) thin provisioning and how to manage the amount of storage allocated per Org vDC so let’s see how it works.

To demonstrate the thin provisioning feature per Org vDC i created an Org vDC with a storage limit of 20 GB ( approximately 40 GB in total available) and thin provisioning enabled. Fast provisioning was disabled.

Second thing i created 2 vApps, each vApp consists of 1 virtual machine with 1 x 8 GB hard disk each.

These 2 vApps uses approximately 1.63 GB storage each instead of 8 GB storage each because of the thin provisioning feature.

This is good and makes it possible to save storage space.
When trying to create a third vApp, making a copy of vApp_system_16 i get an error:
“The requested operation will exceed the VDC’s storage quota”

vDC does not take into account that the virtual machine hard disk/hard disks are thin provisioned when calculating the “Requested” amount of storage per Org vDC.

The virtual machines hard disks (1 per virtual machine) uses approximately 3.2 GB (1.63 GB each) storage but the requested storage for my Org vDC is 16.5 GB.

vDC uses the requested amount of storage when calculating the storage usage (and available storage) per Org vDC and that is why we can not create another virtual machine.

This means you can not over subscribe storage per Org vDC when specifying a storage limit per storage profile per Org vDC which is:

• equal to or less than 100% for the allocation models “Allocation Pool” and “Reservation Pool”.
  
• not set to Unlimited for the allocation model “Pay-As-You-Go”.

If using storage limits equal to or less than 100%  or not using the Unlimited configuration there is only storage over subscription among the Org vDCs and not within one Org vDC.

You enable storage over subscription within an Org vDC by using one of the following configurations.

1. The allocation models “Allocation Pool” and “Reservation Pool” requires a storage limit per storage profile which is greater than 100 %, maximum value is 10 000%, to enable storage over subscription per storage profile.
2. The allocation model “Pay-As-You-Go” requires the storage limit per storage profile set to unlimited to enable storage over subscription per storage profile.

Conclusion

• The vDC thin provisioning feature by itself does not make it possible to create more virtual machines per Org vDC compared to not using the thin provisioning feature.
• The storage limit configuration per storage profile per Org vDC is what makes it possible to use storage over subscription within an Org vDC.