All data that Altavault ingests must go to either a public or a private cloud, Altavault does not support non-cloud replicating scenarios such as "local only"
But you can configure the eviction policy in a way that data is never evicted from the Altavault cache, that option is called Pinning
See TR-4427-1117 for the Share Management options: A SMB/NFS share can be configured with:
Pinning: Important data that cannot wait for recovery from cloud storage can be made available permanently on the AltaVault cache by using this option. Data is never eligible for eviction from the AltaVault appliance cache.