vsphere-esxi-vcenter-server-55-storage-guide

vSphere StorageSharing a VMFS Datastore Across HostsAs a cluster file system, VMFS lets multiple ESXi hosts access the same VMFS datastore concurrently. Youcan connect up to 128 hosts to a single VMFS datastore.Figure 16‐1. Sharing a VMFS Datastore Across HostshostAhostBhostCVM1 VM2 VM3VMFS volumedisk1disk2disk3virtualdiskfilesTo ensure that the same virtual machine is not accessed by multiple servers at the same time, VMFSprovides on-disk locking.Sharing the same VMFS volume across multiple hosts offers the following advantages:• You can use VMware Distributed Resource Scheduling (DRS) and VMware High Availability (HA).You can distribute virtual machines across different physical servers. That means you run a mix ofvirtual machines on each server so that not all experience high demand in the same area at the sametime. If a server fails, you can restart virtual machines on another physical server. In case of a failure,the on-disk lock for each virtual machine is released. For more information about VMware DRS, see thevSphere Resource Management documentation. For information about VMware HA, see the vSphereAvailability documentation.• You can use vMotion to migrate running virtual machines from one physical server to another. Tosupport vMotion between ESXi 5 and version 3.x or 4.x hosts, virtual machines must be located onVMFS3 volumes. For information about migrating virtual machines, see the vCenter Server and HostManagement documentation.VMFS Metadata UpdatesA VMFS datastore holds virtual machine files, directories, symbolic links, RDM descriptor files, and so on.The datastore also maintains a consistent view of all the mapping information for these objects. Thismapping information is called metadata.Metadata is updated each time you perform datastore or virtual machine management operations. Examplesof operations requiring metadata updates include the following:• Creating, growing, or locking a virtual machine file• Changing a file's attributes• Powering a virtual machine on or off• Creating or deleting a VMFS datastore• Expanding a VMFS datastore136 VMware, Inc.