Top 10 Things to Know before upgrading to SharePoint Server 2010

To ensure a smooth upgrade from Microsoft Office SharePoint Server 2007 to Microsoft SharePoint Server 2010, follow these best practices:

  1.  Update your servers to Service Pack 2 (SP2) of Microsoft Office SharePoint Server 2007 or later.Your environment must be updated to Service Pack 2 of Office SharePoint Server 2007 to run the upgrade process, either for an in-place or database attach upgrade. We recommend that you install the October 2009 Cumulative Update because it includes improvements to the pre-upgrade checker tool. For more information about how to install service packs and updates, see the Updates Resource Center for SharePoint Products and Technologies. For a list of all available updates, see Update Center for Microsoft Office, Office Servers, and Related Products.
  2.  Ensure that the environment is fully functioning before you perform an upgrade.An upgrade does not solve any problems that might already exist in your environment. Therefore, ensure that the environment is fully functioning before you perform an upgrade. For example, if you have Web applications that are no longer being used, unextend them before you upgrade. If you want to delete a Web application in Internet Information Services (IIS), unextend the Web application before you delete it; otherwise, SharePoint Server 2010 will try to upgrade the Web application even though it does not exist, and the upgrade will fail. If you find and solve problems beforehand, you are more likely to meet the upgrade schedule that you have estimated.
  3.  Before you try an in-place upgrade, migrate to 64-bit servers. Upgrade your operating system to a 64-bit version of Windows Server 2008 R2 or Windows Server 2008 with Service Pack 2 (SP2). If you are using SQL Server, upgrade or migrate to a 64-bit version of Microsoft SQL Server 2008 R2, SQL Server 2008 with Service Pack 1 (SP1) and Cumulative Update 2, or SQL Server 2005 with SP3 and Cumulative Update 3.Do not try to combine these operations with your upgrade process. You cannot perform an in-place upgrade unless your system already runs on a supported operating system and platform. For more information, see What’s new in upgrade (SharePoint Server 2010).
  4.  Run the pre-upgrade checker to look for potential issues.The pre-upgrade checker reports missing customizations and issues with orphaned sites, and more, so that you can address these issues before you perform your upgrade. For more information, see Run the pre-upgrade checker (SharePoint Server 2010).
  5.  Perform a trial upgrade on a test farm first.Back up the live farm, restore to test servers, and then perform the upgrade. Examine the results to set expectations for what the live upgraded sites will look like, to determine how much post-upgrade customization will have to be done, and to estimate how long the upgrade will take. Try a full search indexing crawl. For more information, see Use a trial upgrade to find potential issues (SharePoint Server 2010).
  6.  Plan for capacity.Ensure that you have disk, processor, and memory capacity sufficient to handle upgrade requirements. For more information about system requirements, see Review system requirements for upgrade (SharePoint Server 2010). For more information about how to plan the disk space that is required for upgrade, see Estimate how long the upgrade process will take and the space that you need (SharePoint Server 2010). For more information about how to plan for capacity, see Performance and capacity management (SharePoint Server 2010).
  7.  Back up your environment.Perform a full backup of your environment before upgrading. That way, you can recover your environment if you must roll back from an upgrade. For more information, see Back up the entire environment before an in-place upgrade (SharePoint Server 2010).
  8.  (Optional) If you are using the database attach upgrade method, set the original databases to read-only.If you expect a long outage window while you perform a database attach upgrade, you can set the databases in the original environment to be read-only so that users can continue to access their data without changing it. For more information, see Attach databases and upgrade to SharePoint Server 2010.
  9.  Do not add any servers to your server farm after you begin the upgrade process.Running the SharePoint Products Configuration Wizard upgrades the configuration database. The configuration database contains the list of servers in the farm. Servers added to the farm after the configuration wizard has been run are not included in the database. Therefore, servers added after the wizard runs do not appear in the upgraded version topology. If you need to add servers to your farm, do so either before you start the upgrade or after you have completed the upgrade process.
  10.   After upgrade, review the Upgrade Status page and upgrade logs to determine whether there are issues that must be addressed. Then review the upgraded sites.The Upgrade Status page reports on the upgrade progress, and the upgrade logs list any errors or warnings that occurred during the upgrade process. You should verify all of the sites and test them before you consider the upgrade complete. For more information, see Verify upgrade and review upgraded sites (SharePoint Server 2010).

Source : Review upgrade best practices (SharePoint Server 2010)