At which level you can apply a backup policy?

You can apply a backup policy at the datastore level, as this is the level at which HPE SimpliVity manages the virtual machines and their backups1. A backup policy consists of one or more rules that specify the destination, frequency, and retention of the backups. You can assign a backup policy to a datastore, and all the virtual machines in that datastore will inherit the backup policy. You can also override the backup policy for individual virtual machines, if needed2. Applying a backup policy at the cluster level (option A), the datacenter level (option B), or the vCenter Server level (option C) is not possible, as these are not the levels at which HPE SimpliVity manages the virtual machines and their backups. These levels are used for organizing and managing the ESXi hosts and the HPE SimpliVity nodes, but not for applying backup policies. References:

1: Using HPE SimpliVity Official Certification Study Guide (HPE2-K45), HPE Press, 2019, p. 28.

2: HPE SimpliVity OmniStack Interoperability Guide 4.2.0, HPE, 2021, p. 8.