Blog post

1.3.3 – Describe storage policies

The policies control which type of storage is provided for the virtual machine and how the virtual machine is placed within storage. Storage policies define how objects that are included in a VM are stored.

There are default storage policies but there also is the possibility to create your own storage policies. You apply the storage policy when you create, clone or migrate a virtual machine.

  • Based on storage capabilities
  • Defined for a VM or disk at deployment
  • Can be applied later
  • Can be changed at any time
  • Cannot be deleted if in use

These are a set of rules which are configured for VMs. VMs need to meet the capabilities of these policies (availability, performance, storage) and it’s best practice to create these policies before you create VMs

VM Storage policies for host-based data services are rules for services provided by your ESXi host.

VM storage policies for vVols are a set of rules for VMs that apply to your vVols datastores.

Rules can be tagged which means that if you assign a tag to the datastore, they automatically get the storage policies.

VSan specific storage policies

  • Primary level of failures to tolerate (PFTT)
    • Defines how many hosts and devices failures VM objects can survive
  • Secondary level of failures to tolerate (SFTT)
    • Defines how many additional host failures can be tolerated after you have a site failure
  • Data locality
    • Allows objects to be limited to one site or one host in stretched clusters environment
  • Failure Tolerance Method
    • Defines data replication mechanisms, (RAID 1, RAID 5, …)
  • Number of disk stripes per object
    • Number of capacity devices where each VM replica is striped.
  • Flash Read cache reservation
    • Defines the size of flash capacity reservation for VM object caching
  • Force Provisioning
    • The policy forces provisioning of objects even when policy cannot be met.
  • Object Space Reservation
    • Percentage of VMDK objects that must be thick provisioned on deployment
  • Disable object checksum
    • Makes sure that the copies of data spread across vSAN cluster are identical