According to the Nutanix Community1, host maintenance mode is used to safely migrate all the user virtual machines (VMs) in the host and make sure no VMs are running on the node. If a VM can't be migrated to another host, you need to shut down the VM for the host to enter into maintenance mode.
According to The Virtualist2, a storage container is a logical segmentation of a storage pool that can be mounted as an NFS datastore on ESXi hosts. You can choose a replication factor (RF) for each storage container, which determines how many copies of data are stored across different nodes.