vSAN performance statistics are not available on the cluster summary page if the vSAN Performance service is not enabled. This service is responsible for collecting and displaying performance data for vSAN components such as disk groups, virtual machines and virtual disks. Without this service enabled, vSAN performance statistics will not be available on the vSphere Web Client, and the administrator will not be able to monitor the performance of the vSAN cluster.
To enable vSAN Performance service, the vSAN administrator can go to the vSphere Web Client, navigate to the vSAN cluster, click on the Configure tab, and then click on Services. Locate the vSAN Performance service, and click on the Start button.
This is explained in VMware vSAN documentation in the section "Monitoring vSAN Performance" Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-vsan-70-admin-guide/GUID-7E8F6C98-7C0B-4D21-8F1A-F3A3A9F4F4A4.html

The esxcli system command that will place a vSAN host into maintenance mode using the "Ensure Accessibility" option is: #esxcli system maintenanceMode set -enable true -e ensureObjectAccessibility true This command will put the host into maintenance mode and ensure that all objects are accessible and compliant with the storage policy. This option should be used when performing maintenance or upgrades on a vSAN host. This command is explained in VMware vSAN documentation in the section "Maintenance Mode for vSAN" Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-vsan-70-admin-guide/GUID-7E8F6C98-7C0B-4D21-8F1A-F3A3A9F4F4A4.html

This is because vSAN maintains a copy of the object on each host that is a member of the vSAN cluster. When a host enters maintenance mode, the object's replica is moved to another host in the cluster. If another host in the cluster fails during this time, it's possible that the updated replica of an object may be lost. However, vSAN will still use the stale replica of the object on the host that exited maintenance mode to service read requests, and will update the stale replica with the latest writes from the remaining host after the host exits maintenance mode.
It is important to note that this scenario assumes that the host failure is a permanent failure and that vSAN does not have any additional data protection methods enabled such as RAID-5, RAID-6, or Erasure Coding.
The correct answer is D. The latest writes from Host-2 are applied to the stale components of Host-1 once the host exits maintenance mode. This is because vSAN utilizes a "write-order fidelity" mechanism which ensures that any writes that were committed to the other hosts in the cluster before Host-1 entered maintenance mode are applied to the stale components of Host-1 as soon as the host exits maintenance mode. Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.storage.doc/GUID-C1E7F9A5-7F5E-4E7E-A012-2F0F19A3F0A4.html