Product Announcements

Migrating to ESXi part 3 – Installing ESXi and reconfiguring the host

This is the third post in my migrating to ESXi series.  In the first post I talked about the need to upgrade vCenter and provided some tips to ensure a smooth upgrade.  In the second post I talked about the need to evacuate VMs off the ESX host and called out special consideration needed for VMs running on boot disk and other local datastores.  This time I will talk about the steps to install ESXi and reconfigure the host after the ESXi migration.

Installing ESXi
Once vCenter has been upgraded and all the VMs have been migrated off your ESX hosts you are ready to install ESXi.  To install ESXi you simply boot the host from the ESXi installation media and follow the prompts to accept the license agreement and select the target boot disk. 


I strongly recommend that before installing ESXi you take some time to document the ESX host configuration using the Host Configuration Worksheet as a guide.  This will ensure you have a good reference available to facilitate reconfiguring the host after the ESXi install.

When installing ESXi there a few things to watch for:

  • Remember, the ESXi install will reformat the boot disk, so make sure you've migrated any VMs and templates you want to keep off the boot disk before you install.
  • Any local disks that the installer identifies as blank (disks without a partition table) will automatically be claimed by ESXi and formatted with VMFS.  If you have any local disks that are blank that you don’t want to have formatted as VMFS disconnect them while you install ESXi. 
  • If the host has access to a large number of LUNs it may take several minutes for the installer to complete its storage scan.  You can speed up the installation by disconnecting the host from the SAN while you install ESXi.

Configure the Management Network
After installing ESXi the next step is to logon to the ESXi Direct Console User Interface (DCUI) and set the host’s password and configure the management network.  From the host's console press F2 to access the System Customize screen (shown below).   The first time you log on the root password will be empty so leave it blank when prompted.  Use the DCUI to set the hosts password and configure the management network.


After configuring the management network it’s always a good idea to test network connectivity using the “Test Management Network” option. 

Reconnect the Host in vCenter
Once the root password has been set and the host is connected to the management network the next step is to reconnect the host in vCenter.  Do this by logging onto the vSphere client, right clicking on the host and choosing connect.


When you reconnect the ESXi host you will get a pop-up notifying you that the SSL certificate cannot be verified; this is okay because the host was reinstalled and now has a new SSL certificate. 


Close the SSL error pop-up and provide the ESXi host’s user name and password when prompted, be sure to choose “yes” when asked whether or not to trust the new host certificate.  The host will then be reconnected in vCenter.


Support for Rolling Upgrades
Note that it is supported to have a mix of ESX 3.5, 4.0, 4.1 and ESXi 4.1 hosts in the same cluster.  This support enables you to perform “rolling upgrades”.  A rolling upgrade is when you take one host out of the cluster, migrate it to ESXi, reconnect it to the cluster, and then repeat the procedure for each of the remaining hosts.   One bit of advice when running a mixed cluster, wait until all hosts in the cluster have been migrated to ESXi before provisioning any new VMs or upgrading the VM VMware Tools and hardware versions.  This is a precautionary step done to avoid any potential conflicts that might crop up when running newer versions of VMware Tools and newer hardware versions on older ESX hosts. 

Reconfigure the ESXi Host

With the ESXi host reconnected in vCenter the final step is to reconfigure the newly migrated ESXi hosts.  In my lab this involves setting the NIC teaming properties, adding vSwitches and Port Groups, and reconfiguring NFS datastores.  Depending on your environment this may also include setting up iSCSI initiators and configuring advanced storage settings and multi-pathing policies.  Check your host against the pre-migration settings documented in the Host Configuration Worksheet to ensure everything gets properly reconfigured.    

Using Host Profiles to Reconfigure ESXi Hosts

If you only have a few hosts to migrate then you can probably get buy with manually reconfiguring them.  However, if you have a lot of ESX hosts manually reconfiguring each host individually is not only repetitive but can become time consuming and error prone.  Fortunately, you can automate the host reconfiguration step using vCenter Host Profiles.  Host Profiles are a licensed vCenter feature and you will need to have a valid license to use them, but remember you can leverage the 60-day trial license included with the vCenter 4.1 install/upgrade.  Just be sure to coordinate your ESXi host migrations to take place within the 60-day trial period.

To use Host Profiles you need to start with a fully configured ESXi 4.1 hosts.  This host will be used as a reference host used to create the Host Profile Template.  To create a Host Profile use the vSphere client to perform the following steps:

  1. Right click the reference host and choose “Host Profile -> Create Profile from Host…”
  2. Enter a name and description for the Host Profile and choose “Next”
  3. Verify the name and description and choose “Finish”


(Note that after you create the Host Profile you can modify and further customize it by navigating to "Home" -> "Host Profiles" in the vSphere client.)

Once the Host Profile has been created you can then attach it to each ESXi host after it has been reconnected in vCenter.  Perform the following steps in the vSphere client to attach a Host Profile to a host:

  1. Place the host into maintenance mode by right-clicking the newly connected ESXi host and choosing “Enter Maintenance Mode…”
  2. Right-click the host and choose “Host Profile -> Manage Profile…”.  In the ensuing pop-up choose the Host Profile to be attached.


After the profile has been attached you then apply the profile.  Applying the profile will apply all the configurartion settings saved in the Host Profile to the host.  For host specific settings, like the IP address for the vMotion networks, you will be prompted to provide the required values.  To apply the host profile:

  1. Right-clicking the ESXi 4.1 host and choose “Host Profile -> Manage Profile… -> Apply Profile…”. 
  2. In the ensuing pop-up provide any values for host specific settings and choose “Next”. 
  3. Once all the required values have been provided click "Finish" to apply the changes to the host.  




(Note, in some cases you may need to apply the Host Profile twice as some changes may require  other changes be committed first).

After the Host Profle has been applied take the host out of maintenance mode by right-clicking the host and choosing "Exit Maintenance Mode…".  At this point the host should be fully configured and capable of hosting VMs.  I recommend testing the host by migrating a few less critical VMs first.  Once you are confident the host is working as expected you can then proceed to migrate the next host in the cluster.


Installing ESXi is pretty straightforward.  You simply boot the host using the installation media and follow the prompts.  Remember the install will overwrite the boot disk, so be sure to migrate any VMs or templates off the boot disk before installing.  It is also important to be aware that any local disks that are blank will automatically get formatted by the ESXi installer.  Also, if the host has access to a lot of LUNs you may want to temporarily disconnect it from the SAN to speed up the install by giving the installer less storage to scan.  After ESXi has been installed logon to the DCUI to set the root user password and configure the management network.  Once the host is back on the management network reconnect it in vCenter and complete the configuration.  If you only have a few hosts to migrate you can manually configure each host.  However, if you have a lot of hosts use Host Profiles to automate the reconfiguration.

Related Articles