Datastores

An image datastores is an ESXi datastore that is typically shared between multiple ESXi hosts. The image datastore holds the images for creating virtual machines, Kubernetes clusters, and other resources.

Image Replication and Datastores

A typical installation is to have a small set of image datastores shared between hosts (usually, one image datastore per host) and one or more local datastores on each host.

When you create an image in Photon Controller, you mark it as either ON_DEMAND or EAGER. Both types are transferred to all image datastores in the system. If you specify EAGER, it will also be transferred to all the other datastores in the system. This approach can result in faster VM creation, but it uses more storage.

If you specify ON_DEMAND and the ESXi host that was chosen to host the VM has a datastore in addition to the image datastore, the image will be copied from the image datastore to that datastore. If there is more than one local datastore, a single datastore is chosen. A datastore specified as ON_DEMAND uses less storage, but it takes longer to create the VM.

When you configure Photon Controller, you can specify the set of allowed datastores. If you do not specify the set, Photon Controller uses all the datastore that it finds. Images will only be replicated or copied to the set of allowed datastores.

Datastores attached after the system is installed will be found and will be used if they are allowed.

It is acceptable to have only one datastore in your deployment as along as it is shared across all hosts. A single, shared datastore is a simple setup because it does not require any replication, but it does require that your datastore can support the the load that will be placed on it.