What cluster file system is utilized by ESXi hosts for storing virtual machines?

VMFS, or Virtual Machine File System, is the specialized cluster file system used by ESXi hosts to store virtual machines. This file system is designed to enable multiple ESXi hosts to share access to the same storage devices, which allows for features such as VMotion and distributed resource scheduling. VMFS is optimized for virtual machine workloads, providing efficient performance and ensuring data integrity in a multi-host environment by managing metadata, facilitating locking mechanisms, and supporting features like snapshots.

In contrast, the other options serve different purposes. SMB (Server Message Block) is a network file sharing protocol mainly designed for providing shared access to files and printers across a network. NFS (Network File System) is another network file system protocol that allows for file sharing over a network but is not specifically optimized for VMware's requirements like VMFS. SCSI (Small Computer System Interface) refers to a standard interface used for connecting and transferring data between computers and peripheral devices but is not a file system in itself.

Thus, VMFS is the correct choice for storing virtual machines in environments utilizing ESXi hosts.