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.
![](https://www.softwaredefinedblog.com/wp-content/uploads/2021/04/Screen-Shot-2021-04-16-at-14.09.51-1024x587.png)
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.
![](https://www.softwaredefinedblog.com/wp-content/uploads/2021/04/Screen-Shot-2021-04-16-at-14.11.08-1-1024x662.png)
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.
![](https://www.softwaredefinedblog.com/wp-content/uploads/2021/04/Screen-Shot-2021-04-16-at-14.13.41-1-1024x337.png)
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.
![](https://www.softwaredefinedblog.com/wp-content/uploads/2021/04/Screen-Shot-2021-04-16-at-14.14.42-1-1024x859.png)
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.