To configure a Windows Server Failover Cluster, what type of disk must be configured and attached to all VMs in the cluster?

In a Windows Server Failover Cluster, a specific type of disk is essential for the cluster's functionality, which is a shared disk. Shared disks allow multiple virtual machines to access the same storage simultaneously, necessary for shared data access.

RDM (Raw Device Mapping) disks are particularly suited for this environment as they provide a way to map a physical disk directly to a virtual machine, allowing shared access among the nodes in a failover cluster while retaining the benefits of VMware's infrastructure. Using RDM allows the VMs to have direct access to a SAN disk, which can enhance performance and enable cluster services that require direct disk access.

Using other types of disk configurations, like thin provisioned disks or regular VMDK disks, does not fulfill the requirements of a failover cluster setup because they do not support shared access in the same way that RDM disks do. Therefore, for a Windows Server Failover Cluster to function properly, RDM disks are the correct choice as they facilitate the necessary shared disk setup needed for cluster operations.