VMware Horizon 5.2: Space Reserved For Expansion Of VMs

When a new VMware Horizon Pool gets created and an error occurs while deploying the Virtual Machines, the only thing you can see under Inventory -> Pools is a small X next to the pool name.

Screen Shot 2015-04-08 at 2.40.15 PM


Once you select the pool and edit it, you can see the pool’s settings and also any errors:

Horizon View - Error During Provisioning


Error during provisioning: Datastores unable to accommodate the new virtual machine because of one or more errors. Space reserved for expansion of VMs. VMware has a great article about this error, which can be found here.

This error does only happen when creating linked clones.
Starting with Horizon View 5.2, View Administrator checks the total total used space on a datastore does not exceed the storage overcommit level you selected for the datastore.

From VMware’s knowledge base article #2047492:

How Horizon View 5.2 or later selects datastores for linked clones

Datastore selection in Horizon View is based on the virtual machine population density. An easy way to think about population density is as a ratio of the amount of used space to the total effective capacity.

The used space contains not only the amount of space that is currently occupied on disk, but also the space needed to power on the provisioned virtual machines. Horizon View makes additional adjustments to the used space calculation to make better decisions in a real Horizon View environment. The total effective capacity is the total size of the datastore multiplied by the overcommit level.
Population density is defined in this formula:

population density = virtual used space / (total datastore capacity * overcommit level)
During provisioning or rebalance operations, Horizon View selects the datastore with the least population density.

Overcommit levels are defined in this table:

Option Storage Overcommit Level
None Storage is not overcommitted.
Conservative 4 times the size of the datastore. This is the default level.
Moderate 7 times the size of the datastore.
Aggressive 15 times the size of the datastore.
Unbounded View Manager does not limit the number of linked-clone desktops that it creates based on the physical capacity of the datastore. It is up to you to calculate the space and determine that the number of virtual machines you want to place can be supported by the datastore.*

* Select Unbounded only if you manage your own linked-clone desktops.

The Storage Overcommit level can be set when you create a new pool and select the datastore. When setting Storage Overcommit to Unbounded, Horizon View will not limit the number of linked clones based on the physical capacity of the datastore.

Horizon View Storage Overcommit