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

vSphere StorageIf a host contributes its local storage to the Virtual SAN datastore, the host must provide at least one HDD,also called data disk, and at least one SSD. The disks on the contributing host form a disk group, whichincludes one SSD and at least one or multiple data disks. The disk group uses the SSD disk for read cachingand write buffering, while the data disks are used for persistent storage. You can have multiple disk groupsper host. For example, in the illustration, host 1 contains one disk group, while host 3 has two disk groups.VM VM VM VM VM VM VMHost 1 Host 2 Host 3Virtual SAN datastoreSSD disksDisk group 1 Disk group 2 Disk group 3Data disksVirtual SAN and Virtual Machine Storage PoliciesWhen enabled, Virtual SAN works together with virtual machine storage policies. You use storage policiesto define virtual machine storage requirements such as performance and availability in the form of a profile.The policy requirements are pushed to the Virtual SAN layer when the virtual disk is created. Virtual SANlays out the virtual disk across the Virtual SAN datastore to meet the specified requirements.Virtual SAN monitors and reports on the policy compliance during the lifecycle of the virtual machine. Ifthe policy becomes noncompliant because of a host, disk, or network failure, or workload changes, VirtualSAN takes remedial actions. It reconfigures the data of the affected virtual machines and optimizes the useof resources across the cluster. Any reconfiguration processes occur with minimal impact on the regularworkload.For information on how Virtual SAN and virtual machine storage profiles interact, see “Virtual SAN andStorage Policy-Based Management,” on page 188.For general information about storage policies, see Chapter 20, “About Virtual Machine Storage Policies,” onpage 195.Virtual SAN and Object-Based StorageVirtual SAN stores and manages data in the form of flexible data containers called objects. An object is alogical volume that has its data and metadata distributed and accessed across the entire cluster.When you provision a virtual machine on a Virtual SAN datastore, Virtual SAN creates an object for eachvirtual disk. It also creates a container object that stores all metadata files of the virtual machine. VirtualSAN can store and manage multiple objects in a single cluster.174 VMware, Inc.