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.

Note: All of these fixes will be included in Office 2007 SP2 (and as a bit of historical trivia, all of these fixes were originally intended for SP2, but based on their quality and the rigorous testing that has been done with them, the Outlook team made the decision to backport the SP2 work into this cumulative update so that you, our customers, can take advantage of the changes sooner rather than later).

In the past, from an Exchange perspective, we made a statement with regards to the Outlook 2007 Cached Exchange Mode experience (notably in the Mailbox Server Storage Design TechNet article) along the lines of 1 GB mailboxes with around 1 GB RAM requires at least 5400 RPM hard disks, and 2 GB mailboxes with 1-2 GB of RAM requires at least a 7200 RPM hard disk. We also recommended for high performance on mailboxes larger than 2 GB, that you reduce your mailbox size or use Online Mode. This guidance is no longer applicable with the latest product update.

With the release of Outlook 2007 SP1 February 2009 cumulative update, we are updating our Mailbox Storage Sizing Guidance to reflect the improved performance and responsiveness when utilizing Cached Exchange Mode with respect to mailbox/OST sizes:

  • 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.

As a result of this guidance change, you may have a few questions. We've tried to anticipate those questions here and have provided answers. In addition, for more information on troubleshooting Outlook performance issues, please see http://support.microsoft.com/kb/940226.

Question: What if I am using a first generation solid state drive (SSD) or a slow rotational hard disk drive?

If you are running Outlook 2007 on a computer that has a first generation solid state drive (SSD) or a slow rotational hard disk drive (HDD), you may experience frequent pauses when you perform typical operations in Outlook (especially if you have not installed the February 2009 cumulative update).

Storing and retrieving data in an Outlook data file involves a high number of small noncontiguous reads and writes. A good metric to use when gauging data file performance on specific hardware is the disk drive's noncontiguous write performance. The Windows performance team has provided a tool named WinSAT (see below for download and KB 940226 as well as WinSAT documentation for execution instructions) that can be used to benchmark specific disk drives. As you can see in the table below, the estimated experience for Outlook 2007 SP1 with the February 2009 cumulative update is better.

The WinSAT tool is part of the Windows Vista Upgrade Advisor, and is included in Windows Vista. For non Windows Vista machines, you can download the Windows Vista Upgrade Advisor here:

http://www.microsoft.com/downloads/details.aspx?FamilyId=42B5AC83-C24F-4863-A389-3FFC194924F8&displaylang=en

The following table shows an estimated Outlook experience based on the score returned by the WinSAT tool (again, see KB 940226 as well as WinSAT documentation for execution instructions):

WinSAT score

Drive characteristics

SP1 before Feb update

SP1 after Feb update and later versions

Less than 15 MB/s

Generation 1 and Generation 2 SSDs (early 2008)

Unusable

Reasonable, responsive, limited hangs and pauses

Between 15 MB/s and 30 MB/s

Most Generation 2 SSDs (after April 2008); many 5400 rpm laptop rotational drives

Many hangs and pauses throughout the day

Reasonable, responsive, limited hangs and pauses

Between 30 MB/s and 40 MB/s

Some high-end Generation 2 SSDs (after September 2008); many 7200 rpm rotational drives

Reasonable, responsive, limited hangs and pauses

Quick, responsive, only occasional hangs

Greater than 40 MB/s

Generation 3 SSDs, both MLC and SLC technology (November 2008); many 10000 rpm rotational drives

Quick, responsive, only occasional hangs

Quick, responsive, rarely hangs

Question: What if I have many items in a single folder?

If you have a large number of items in any single folder, you may experience performance issues during certain operations in Outlook while using Cached Exchange mode or using a Personal Folders file. These performance issues are especially noticeable when you switch into and out of that folder:

  • 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.

We recommend that you move several items in these larger folders to separate folders in the same store or to an archive store, and use Arrange By: Date when running Service Pack 1 (SP1) with the February 2009 cumulative update for folders that have a large number of items.

If you are not using Cached Exchange Mode, then please review the following TechNet article Understanding the Performance Impact of High Item Counts and Restricted Views.

If you have any questions, please let us know. The Mailbox Server Storage Design article will be updated in a future TechNet refresh and account for these updated recommendations.

- Ross Smith IV

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