The Pre-Check Remediation is a check that is performed on the host or the cluster that displays a table that lists possible problems that might prevent a successful remediation, and a recommendation on how to fix the issues.

When you generate a pre-check remediation report, Update Manager generates a list with recommended actions you must perform to ensure a successful remediation of the hosts in your cluster.

You can generate a pre-check remediation report from both vSphere Client and the vSphere Web Client.

From the vSphere Client, you can generate a pre-check remediation report by selecting a host or a cluster from the inventory, and navigating to the Updates tab. In the top-right corner, there is a pre-check remediation card from where you can generate the report.

From the vSphere Web Client, you can generate a pre-check remediation report when you create a remediation task for hosts that are contained in a cluster. You generate the report from the Cluster Remediation Options page of the Remediate wizard.

Table 1. Pre-Check Remediation Report for Clusters
Current Configuration/Issue Recommended action Details
Is DPM disabled? Disable DPM on the cluster. If a host has no running virtual machines, DPM might put the host in standby mode before or during remediation and Update Manager cannot remediate them. Disable DPM on a cluster to ensure that the remediation process is successful.
Is DRS enabled? Enable DRS on the cluster. DRS enables vCenter Server to place and migrate virtual machines automatically on hosts to attain the best use of cluster resources.
Is HA admission control disabled? Disable HA admission control. HA admission control prevents migration of the virtual machines with vMotion and the hosts cannot enter maintenance mode. Disable HA admission control on a cluster to make sure that remediation is successful.
Is EVC disabled on the cluster? Enable EVC on the cluster. EVC helps ensure vMotion compatibility between hosts in a cluster. When enabled on compatible hosts, EVC ensures that all hosts in a cluster present a common set of CPU features to virtual machines. EVC must be enabled so that the virtual machines are migrated successfully within the cluster during remediation.
Is vSAN health check successful? Navigate to vSAN Health page and address any health issues before proceeding with remediation. The vSAN health check performs a series of tests on the hosts in the vSAN cluster. The vSAN health check must succeed to ensure successful remediation of hosts in the vSAN cluster. If you start a remediation task in a vSAN cluster that failed the vSAN health check in the pre-check remediation report, the hosts enter maintenance mode, get upgraded, but might fail to exit maintenance mode, and the remediation eventually fails.
Table 2. Pre-Check Remediation Report for Virtual Machines
Current Configuration/Issue Changes applied for remediation Details
A CD/DVD drive is attached. Disconnect the CD/DVD drive. Any CD/DVD drives or removable devices connected to the virtual machines on a host might prevent the host from entering maintenance mode. When you start a remediation operation, the hosts with virtual machines to which removable devices are connected are not remediated.
A floppy drive is attached. Disconnect the floppy drive. Any floppy drives or removable devices connected to the virtual machines on a host might prevent the host from entering maintenance mode. When you start a remediation operation, the hosts with virtual machines to which removable devices are connected are not remediated.
FT is enabled for a VM on a host in the cluster. FT prevents successful remediation. Disable FT on the virtual machine. If FT is enabled on for any of the virtual machines on a host, Update Manager cannot remediate that host.
VMware vCenter Server is installed on the virtual machine and DRS is disabled on the cluster. Enable DRS on the cluster and ensure that virtual machines can be migrated with vMotion. One of the virtual machines in the cluster runs the vCenter Server instance that you currently use. If you enable DRS on the cluster, vMotion can migrate the VM where vCenter Server runs to ensure that the remediation process of the hosts in the cluster is successful.
VMware vSphere Update Manager is installed on the virtual machine and DRS is disabled on the cluster. Enable DRS on the cluster and ensure that virtual machines can be migrated with vMotion. One of the virtual machines in the cluster runs the Update Manager instance that you currently use. If you enable DRS on the cluster, vMotion can migrate the VM where Update Manager runs to ensure that the remediation process of the hosts in the cluster is successful.