You can place View Composer replicas and linked clones on separate datastores with different performance characteristics. This flexible configuration can speed up intensive operations such as provisioning many linked clones at once or running antivirus scans.
For example, you can store the replica virtual machines on a solid-state disk-backed datastore. Solid-state disks have low storage capacity and high read performance, typically supporting 20,000 I/Os per second (IOPS). View Composer creates only one replica for each View Composer base-image snapshot on each ESXi cluster, so replicas do not require much storage space. A solid-state disk can improve the speed at which ESXi reads a replica's OS disk when a task is performed concurrently on many linked clones.
You can store linked clones on traditional, spinning media-backed datastores. These disks provide lower performance, typically supporting 200 IOPS. They are cheap and provide high storage capacity, which makes them suited for storing the many linked clones in a large pool. ESXi does not need to perform intensive, simultaneous read operations on a linked clone.
Configuring replicas and linked clones in this way can reduce the impact of I/O storms that occur when many linked clones are created at once. For example, if you deploy a floating-assignment pool with a delete-machine-on-logoff policy, and your users start work at the same time, View must concurrently provision new machines for them.
This feature is designed for specific storage configurations provided by vendors who offer high-performance disk solutions. Do not store replicas on a separate datastore if your storage hardware does not support high-read performance.
You must follow certain requirements when you store the replica and linked clones in a pool on separate datastores:
You can specify only one separate replica datastore for a pool.
If a replica datastore is shared, it must be accessible from all ESXi hosts in the cluster.
If the linked-clone datastores are shared, the replica datastore must be shared. The replica cannot reside on a local datastore.
If the linked-clone datastores are local, VMware strongly recommends that you store the replica on the same volume as the linked clones. Although it is possible to store linked clones on local datastores and the replica on a shared datastore if all ESXi hosts in the cluster can access the replica, VMware does not recommend this configuration.
This feature is not available you use Virtual SAN datastores or Virtual Volumes datastores. These types of datastores use Software Policy-Based Management, so that storage profiles define which components go on which types of disks.