When you create or edit an instant-clone desktop pool, the Select Instant Clone Datastores page displays a table that provides storage-sizing guidelines. The table can help you to decide which datastores to select for the instant-clone disks. The guidelines calculate space needed for new clones.

Sizing Table for OS Disks

Example Sizing Table for OS Disks shows an example of storage-sizing recommendations that might be displayed for a pool of 10 virtual machines if the golden image virtual machine has 1GB of memory and a 10GB replica.

Table 1. Example Sizing Table for OS Disks
Data Type Selected Free Space (GB) Min Recommended (GB) 50% Utilization (GB) Max Recommended (GB)
OS disks 184.23 40.00 80.00 130.00

The Selected Free Space column shows the total available space on all of the datastores that you selected for a disk type such as OS disks.

The Min Recommended column shows the minimum amount of recommended storage for a pool.

The 50% Utilization column shows the recommended storage when the disks grow to 50% of the golden image.

The Max Recommended column shows the recommended storage when the disks approach the full size of the golden image.

Horizon estimates the storage space that is needed for new clones. When you create a desktop pool, the sizing guidelines encompass the entire pool. When you edit an existing desktop pool, the guidelines encompass only the new clones that you add to the pool.

For example, if you add 100 clones to a desktop pool and select a new datastore, Horizon estimates space requirements for the 100 new clones. If you select a new datastore but keep the desktop pool the same size, or reduce the number of clones, the sizing guidelines show 0. The value of 0 reflect that no new clones must be created on the selected datastore. Space requirements for the existing clones are already accounted for.

How Horizon Calculates the Minimum Sizing Recommendations

To arrive at a minimum recommendation for OS disks, Horizon estimates that each clone consumes twice its memory size when it is first created and started up. If no memory is reserved for a clone, an ESXi swap file is created for a clone as soon as it is powered on. The size of the guest operating system's paging file also affects the growth of a clone's OS disk.

In the minimum recommendation for OS disks, Horizon also includes space for two replicas on each datastore. Horizon creates one replica when a pool is created. When the instant-clone pool is patched for the first time by a push image, Horizon creates a second replica on the datastore, anchors the clones to the new replica, and deletes the first replica if no other clones are using original snapshot. The datastore must have the capacity to store two replicas during the recompose operation.

By default, replicas use vSphere thin provisioning, but to keep the guidelines simple, Horizon accounts for two replicas that use the same space as the golden image virtual machine.

To arrive at a minimum recommendation storing replicas on a separate datastore, Horizon allows space for two replicas on the datastore. The same value is calculated for minimum and maximum usage.

For details, see Storage Sizing Formulas for Instant-Clone Desktop Pools.