OST Sizing Guidance Changes

EDIT 3/24/2009: Added a link to WinSAT documentation based on reader feedback. Hopefully you have seen the news regarding the release of the Outlook 2007 SP1 February 2009 cumulative update. If you haven't, then you can read http://support.microsoft.com/?id=968009 for all the detail, but basically we have made significant improvements in terms of Outlook's performance and responsiveness:

• General Responsiveness - the Outlook 2007 SP1 February 2009 cumulative update reduces I/O disk usage and UI response time.
• Startup - the Outlook 2007 SP1 February 2009 cumulative update removes long operations from initial startup (please note that there is a one-time data structure upgrade cost after the first install that takes a relatively linear amount of time based on the size of your PSTs and OST).
• Shutdown - the Outlook 2007 SP1 February 2009 cumulative update makes Outlook exit predictably despite pending activities (for more information, please see http://msdn.microsoft.com/en-us/library/dd239276.aspx).
• Folder/View Switch - the Outlook 2007 SP1 February 2009 cumulative update improves view rendering and folder switching.

• Up to 5 gigabytes (GB): This size should provide a good user experience on most hardware.
• Between 5 GB and 10 GB: This size is typically hardware dependent. Therefore, if you have a fast hard disk and much RAM, your experience will be better. However, slower hard drives, such as drives that are typically found on portable computers or early generation solid state drives (SSDs), experience some application pauses when the drives respond.
• More than 10 GB: This size is where short pauses begin to occur on most hardware.
• Very large, such as 25 GB or larger: This size increases the frequency of the short pauses, especially while you are downloading new e-mail. Alternatively, you can use Send/Receive groups to manually sync your mail.

• When you use Outlook 2007 with the Performance Update, or you use Outlook 2007 SP1 versions before the February 2009 cumulative update, generally, when 10,000 or more items are in a single folder, these issues can occur.
• When you use Outlook 2007 SP1 with the February 2009 cumulative update or higher and have more than 50,000 items in a single folder, views other than Arranged By: Date can be slower.