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

vSphere StorageVirtual SAN and Storage Policy-Based ManagementWhen you use Virtual SAN, you can define virtual machine storage requirements, such as performance andavailability, in the form of a policy profile. The policy requirements are then pushed down to the VirtualSAN layer when a virtual machine is being created. The virtual disk is distributed across the Virtual SANdatastore to meet the requirements.When you enable Virtual SAN on a host cluster, a single Virtual SAN datastore is created. In addition,enabling Virtual SAN configures and registers the Virtual SAN storage provider that uses VASA tocommunicate a set of the datastore capabilities to vCenter Server.A storage capability is typically represented by a key-value pair, where the key is a specific property that thedatastore can offer and the value is a metric, or a range, that the datastore guarantees for a provisionedobject, such as a virtual machine metadata object or a virtual disk.When you know storage requirements of your virtual machines, you can create a storage policy referencingcapabilities that the datastore advertises. You can create several policies to capture different types or classesof requirements.You can apply these storage policies when you create or edit virtual machines.NOTE If you do not apply a storage policy to a virtual machine, it will use a default Virtual SAN policy withone number of failures to tolerate and a single disk stripe per object.Table 19‐2. Storage Policy AttributesCapabilityNumber of failures to tolerateNumber of disk stripes per objectObject space reservationDescriptionDefines the number of host, disk, or network failures avirtual machine object can tolerate. For n failures tolerated,n+1 copies of the virtual machine object are created and 2n+1 hosts with storage are required.Default value is 1. Maximum value is 3.The number of HDDs across which each replica of a virtualmachine object is striped. A value higher than 1 mightresult in better performance, but also results in higher useof system resources.Default value is 1. Maximum value is 12.Percentage of the logical size of the object that should bereserved, or thick provisioned, during virtual machinecreation. The rest of the storage object is thin provisioned.This value applies only when you chose thin provisioningfor a virtual disk. If your disk is thick provisioned, 100% isreserved automatically.Default value is 0%. Maximum value is 100%.188 VMware, Inc.