If two hosts in a four-node vSAN cluster are down, the cluster might experience data loss because the default storage policy has a Primary level of failures to tolerate (PFTT) of 1, which means that vSAN can tolerate only one host failure. The Ensure accessibility maintenance mode option does not guarantee full data redundancy, but only ensures that all accessible VMs remain accessible. If another host fails while one host is in maintenance mode, some VMs might lose access to their data components and become unavailable or corrupted. References:  vSAN Maintenance Mode Options ;  vSAN Cluster Configuration Limits

Utilizing Network I/O Control and isolating vSAN traffic in a VLAN are the two actions that should be taken to configure the new vSAN cluster to meet the requirements. Network I/O Control allows the vSAN administrator to create network resource pools and assign bandwidth shares or reservations to different traffic types, such as vSAN, vMotion, or management. This ensures that vSAN traffic has guaranteed bandwidth during contention and can achieve better performance and availability. Isolating vSAN traffic in a VLAN enhances the security of the cluster by preventing unauthorized access or interference from other network segments. It also simplifies the network configuration and management by reducing the broadcast domain and avoiding IP address conflicts. Creating static routes between the vSAN hosts, using IOPS Limit rules in storage policies, and enabling jumbo frames are not necessary or recommended actions for this scenario. Static routes are not required for vSAN communication, as vSAN uses multicast or unicast depending on the version and configuration. IOPS Limit rules are used to limit the IOPS allocated to an object, which can degrade the performance and latency of the application. Jumbo frames can improve the network efficiency and throughput, but they are not mandatory for vSAN and require consistent configuration across all network devices. References:

Network I/O Control

vSAN Network Design Guide