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Outlook 365 multiple OST files

Andrew Gresbach1709152664


As we are working on migrating our mailboxes to our 365 cloud server we needed to enabled cached mode otherwise Outlook performance was unusable.  It creates the ost file and works fine, however 1 week in and we're getting lots of people that we noticed were running out of free space in their user layer.  Further investigation showed that their ost file was being recreated multiple times for some reason.  The user would not get any alert in Outlook that there was an issue like a typical corrupted ost symptom would give but just they'd notice Outlook would show that it was downloading their inbox all over again.   Has anyone else run into this?  its been pretty random on when/who it hits so no noticable patterns yet......some users are good between reboots no problem using the same ost and some have 5 copies of theirs

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Are you using Full User Layers, or are you using our Office 365 User Layers?  If you're using the O365 User Layers, you absolutely must have a profile manager involved.  Outlook will create a new OST file if it doesn't remember creating the previous one.  So if you're using our O365UL, Outlook knows it creates the first one, you reboot, and now Outlook doesn't know anything about the old one from the previous boot.  It makes a new one.  We require a profile manager like UPM (now CPM) to give Outlook a place to remember its OST files.


If you're using Full User Layers, then the User Layers themselves should be doing that remembering and I don't have a good answer for why Outlook might not be recognizing your mailbox files.

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With the understanding that I'm just guessing here, I believe that the files are being preserved properly, but the Outlook configuration is not.  That's why Outlook decides it's never seen your mailbox files and re-downloads them.  Does AppSense just capture settings to be applied to users, or does it capture any of the settings once applied?  Like you, I can't imagine what's going wrong when it fails, since it works at least some of the time.  We're generally a lot more predictable than that: if we're going to break something, we break it every time.


Can you try with AppSense disabled, just to see if it's somehow a contributing factor?

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Hi again SocietyInsurance we seem to keep having the same issues. We've also seen this problem and a lot of issues with the Session O365 layer being unable to attach at logon , so many so that we are now looking at switching to the UPM delivered OST.  I can't help but wonder if this issue and the issue we are both facing with BSOD are somehow related.  I did manage to offload my event logs before my last crash and just before the time it failed the logs are riddled with errors about the elastic drives getting lost. 

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thanks for the update!  we were having too many weird outlook issues and this multiple ost issue was getting out of hand so we actually made the call to revert everything back to onprem so we could disable cached mode .  We'll see how things go if it gets any better but i know we've had the lockup issue before we turned cached mode on so i'm not holding out a lot of hope on getting that lucky.     We haven't been able to predict who/when it will happen so still trying to find a way to get the logs you got .   What hypervisor do you use out of curiosity?

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