When you upgrade or migrate hosts, you must understand and follow the best practices process for a successful upgrade or migration.
For a successful upgrade or migration, follow these best practices:
Make sure that you understand the ESXi upgrade process, the effect of that process on your existing deployment, and the preparation required for the upgrade.
If your vSphere system includes VMware solutions or plug-ins, make sure they are compatible with the vCenter Server version that you are upgrading to. See the VMware Product Interoperability Matrix at http://www.vmware.com/resources/compatibility/sim/interop_matrix.php.
Read Preparing to Upgrade Hosts to understand the changes in configuration and partitioning between ESX/ESXi 4.x and ESXi 5.x, the upgrade and migration scenarios that are supported, and the options and tools available to perform the upgrade or migration.
Read the VMware vSphere Release Notes for known installation issues.
If your vSphere installation is in a VMware View environment, see Upgrading vSphere Components Separately in a Horizon View Environment.
Prepare your system for the upgrade.
Make sure your current ESX or ESXi version is supported for migration or upgrade. See Supported Upgrades to ESXi 5.5.x.
Make sure your system hardware complies with ESXi requirements. See System Requirements and the VMware Compatibility Guide, at http://www.vmware.com/resources/compatibility/search.php. Check for system compatibility, I/O compatibility (network and HBA cards), storage compatibility, and backup software compatibility.
Make sure that sufficient disk space is available on the host for the upgrade or migration. Migrating from ESX 4.x to ESXi 5.x requires 50MB of free space on your VMFS datastore.
If a SAN is connected to the host, detach the fibre before continuing with the upgrade or migration. Do not disable HBA cards in the BIOS.Note:
This step does not apply to ESX hosts that boot from the SAN and have the Service Console on the on the SAN LUNs. You can disconnect LUNs that contain the VMFS datastore and do not contain the Service Console.
Back up your host before performing an upgrade or migration, so that, if the upgrade fails, you can restore your host.Important:
Once you have upgraded or migrated your host to ESXi 5.x, you cannot roll back to your version 4.x ESX or ESXi software.
Depending on the upgrade or migration method you choose, you might need to migrate or power off all virtual machines on the host. See the instructions for your upgrade or migration method.
After the upgrade or migration, test the system to ensure that the upgrade or migration completed successfully.
Reapply your host licenses. See Reapplying Licenses After Upgrading to ESXi 5.5.
Consider setting up a syslog server for remote logging, to ensure sufficient disk storage for log files. Setting up logging on a remote host is especially important for hosts with limited local storage. Optionally, you can install the vSphere Syslog Collector to collect logs from all hosts. See Providing Sufficient Space for System Logging. For information about setting up and configuring syslog and a syslog server, setting up syslog from the host profiles interface, and installing vSphere Syslog Collector, see the vSphere Installation and Setup documentation.
If the upgrade or migration was unsuccessful, and you backed up your host, you can restore your host.