Before you upgrade to vCenter Server, make sure your system is properly prepared. To ensure that your system is prepared for the upgrade, read all the subtopics in this section. About the vCenter Server UpgradeVMware supports in-place upgrades on 64-bit systems from vCenter Server 4.x, vCenter Server 5.0.x, and vCenter Server 5.1.x to vCenter Server 5.5. How vCenter Single Sign-On Affects vCenter Server UpgradesWhich users can log in to vCenter Server after an upgrade depends on the version that you are upgrading from and the deployment configuration. vCenter Single Sign-On Deployment ModesvCenter Server provides several ways to deploy vCenter Single Sign-On to best serve your vSphere environment. vCenter Single Sign-On and High AvailabilityvSphere provides several ways to ensure availability of your vSphere deployment with vCenter Single Sign-On. vCenter Single Sign-On ComponentsvCenter Single Sign-On includes the Security Token Service (STS), an administration server, and vCenter Lookup Service, as well as the VMware Directory Service (vmdir). Setting the vCenter Server Administrator UserThe way you set the vCenter Server administrator user depends on your vCenter Single Sign On deployment. Authenticating to the vCenter Server EnvironmentIn vCenter Server versions 5.1 and later, users authenticate through vCenter Single Sign-On. How vCenter Single Sign-On Affects Log In BehaviorvCenter Single Sign-On log in behavior depends on the domain the user belongs to and the identity sources that you have added to vCenter Single Sign-On. Identity Sources for vCenter Server with vCenter Single Sign-OnIdentity sources allow you to attach one or more domains to vCenter Single Sign-On. A domain is a repository for users and groups that the vCenter Single Sign-On server can use for user authentication. vCenter Server Upgrade SummaryThe upgrade to vCenter Server 5.5.x affects other software components of your datacenter. Required Information for Installing or Upgrading vCenter Single Sign-On, Inventory Service, vCenter Server, and the vSphere Web ClientPrepare for the vCenter Server installation by recording the values that vCenter Server and related components require. Best Practices for vCenter Server UpgradesWhen you upgrade vCenter Server, you must understand and follow the best practices process for a successful upgrade. Prerequisites for the vCenter Server UpgradeBefore you begin the upgrade to vCenter Server, make sure you prepare the vCenter Server system and the database. vCenter Server Database Configuration NotesAfter you choose a supported database type, make sure you understand any special configuration requirements. Upgrading to vCenter Server on a Different MachineInstead of performing an in-place upgrade to vCenter Server, you might want to use a different machine for your upgrade. Because vCenter Server 5.x requires a 64-bit platform, you cannot upgrade from a version of vCenter Server installed on a 32-bit platform. Supported Database UpgradesWhen you upgrade to vCenter Server 5.5, make sure that the upgraded version supports your database. Confirm That vCenter Server Can Communicate with the Local DatabaseIf your database is located on the same machine on which vCenter Server will be installed, and you have changed the name of this machine, make sure the vCenter Server DSN is configured to communicate with the new name of the machine. Synchronizing Clocks on the vSphere NetworkBefore you install vCenter Single Sign-On, the vSphere Web Client, or deploy the vCenter Server Appliance, make sure that all machines on the vSphere network have their clocks synchronized. JDBC URL Formats for the vCenter Server DatabaseThe vCenter Server installer generates and validates the JDBC URL for the vCenter Server database. If the installer fails to connect to the database using the generated JDBC URL, the installer will prompt you to specify the JDBC URL. DNS Load Balancing Solutions and vCenter Server Datastore NamingvCenter Server 5.x uses different internal identifiers for datastores than earlier versions of vCenter Server. This change affects the way that you add shared NFS datastores to hosts and can affect upgrades to vCenter Server 5.x. About the vCenter Host Agent Pre-Upgrade CheckerThe vCenter Host Agent Pre-Upgrade Checker produces a report showing known issues that might prevent a successful upgrade of the vCenter Host Agent software. Downtime During the vCenter Server UpgradeWhen you upgrade vCenter Server, downtime is required for vCenter Server. Download the vCenter Server InstallerDownload the installer for vCenter Server, the vSphere Web Client, and associated vCenter components and support tools. Microsoft SQL Database Set to Unsupported Compatibility Mode Causes vCenter Server Installation or Upgrade to FailvCenter Server installation with a Microsoft SQL database fails when the database is set to compatibility mode with an unsupported version.