Duplicate OST files RRS feed

  • Question

  • We have a non-persistent VDI environment setup with O365, and we are using Outlook with cache mode enabled, so we are testing out the FSLogix Office container, and we are just capturing the Outlook cache without the personalization settings.  I have had 7 users test the Outlook caching, and 2 of the users have an issue where their OST files are recreated each time they have a new VDI session and launch Outlook, so it seems Outlook is not loading their existing OST file, but caches a new one instead.

    I've checked the %userprofile%\AppData\Local\Microsoft\Outlook location to confirm that an OST file exists prior to launching Outlook as well, so the OST is being writen to the Office container.  I also watched the VHDX file increase when the additional OST files are created. 

    The VDI machines are using PVS disk streaming, so the VMs are loaded from the same Vdisk, so there is no differences between the machine configurations or O365 installation.

    When I set the VDI environment as persistent and disable FSLogix, then those same two users' OST files do not duplicate.

    Any ideas what would cause the OST file to recreate for some users and not others? Any recommendations for troubleshooting?

    • Edited by petbr3 Thursday, February 20, 2020 8:03 PM
    Thursday, February 20, 2020 8:01 PM


  • Hi petbr3,

    Have a look at this article:


    If you reset the user profile, you delete the outlook profile. When you do this, even though your OST file is still intact in your Office 365 Container, Outlook will not use it on a new profile build and will create a new OST. In Outlook 2013 onwards, you can choose to alter the OST in use and point it back to the existing OST to reuse the cache. Change OST Location

    Hope this helps!

    • Marked as answer by petbr3 Wednesday, February 26, 2020 3:06 PM
    Wednesday, February 26, 2020 11:41 AM