VM snapshots on a vSAN datastore and their SPBM policy

When we create a snapshot of a VM on a vSAN datastore, delta disks (where all new writes go) inherit the storage policy from the base disk.

Our VM Test_VM_123 uses vSAN policy RAID – 1 mirror, which means there are at least two copies of the VMDK and a witness. After snapshot is taken, we see the same policy applied to delta disk.

But if we want to change a storage policy for Test_VM_123, we can change it for a VM Home object and base disk only. There is no option to change the policy for a “snapshot”/delta disk.

After the policy was changed for a base disk to FTT-0/ RAID-0 Stripe 4, we see the delta disk retained its FTT-1 policy.

This behaviour is described in VMware KB 70797 “Modifying storage policy rules on Virtual Machine running on snapshot in vSAN Data-store”. In order to keep all storage policies consistent across VM disks, it is recommended to consolidate all the snapshots before making a SPBM policy changes to a VM.