Microsoft Office (Exchange) 365 - RDSH Myth

· 5 min read
Microsoft Office (Exchange) 365 - RDSH Myth

For many years now, the everything in cloud is happening more and more, among all the services / software available as a services, most of the vendor are promising a cheaper way to manage their software and a much more simple way to manage it..

I know some of you will disagree with what I writing about and some will agree, this is a view from my experience on the field 🙂

A couple of weeks ago I launched a small poll on Twitter asking this question : “Why Do you think companies are moving to Exchange 365 ?” Here are the results :



It’s less complex” won the poll follow by “it’s a fashion” and then “it’s cheaper“… I tend to agree with everything here, because if you get rid of a complete Exchange infrastructure with all the people you need to architecture and manage it, it will be cheaper and less complex for sure ! But this is just a dream without complexity of companies and without user’s usage of their Outlook.

What I try to point here is : Moving to Exchange 365 is not as easy as it seems, some company do have a “basic” Outlook / Exchange usage and it won’t bring issues but most of the companies I saw have had issue because Microsoft and Microsoft’s Partner did not capture the way users were used to work with their Outlook mail software.



The picture above is the “put everything into the Cloud, you will save money” ideal. This ideal is true and can be reached when you know your users work habits and already have an organised mail infrastructure.

But this ideal can be easily broken

If it looks easy on the paper or in a Powerpoint presentation, simple things can break this kind of project into pieces and make it fails.. How ?



Here is a list (to be completed 😀 )

  • Outlook plugins
  • Online Mode
  • RDSH environment
  • Bad Architecture decision / Consulting

Outlook plugins is the work enemy of the Cloudification because it means in 90% of the case you’ll be forced to keep Outlook mail client, it’s a road block for OWA adoption…

Once you’re stuck with the Outlook mail client, you need to deal with the Online or Cache mode with Exchange 365… Piece of cake right ? Workstation / Laptop –> Cache mode enable, no problem ! But what about RDSH environment ? Citrix XenApp / Microsoft RDS or VMware Horizon ?

Now you have RDSH environment and we need to enable cache mode because user are complaining about slowness (even freeze to not responding Outlook). So if we enable the cache mode, what should we do with the OST file ? (up to several Gb per user file) – I come back later on this particular point –

What do you do if your environment has not been properly assess by the architects in charge ? Not enough public IP to connect to Microsoft Exchange 365 infrastructure ? What do you need to do if Outlook user’s habits have been ignored or not well assessed ? There is not much you can do after that except trying to add another layer of “something” to try to fix things…

RDSH world and Exchange 365

I couldn’t resist to post this picture from Microsoft website :



If I translate this picture into words :

With the Cached Exchange Mode enable, you can go to camp in the forest with your laptop making a fire camp Under the moon and the low altitude flying aircraft. All of that Under a tree !

That’s amazing what you can do while using Cached Exchange Mode 🙂 Anyway, joke aside, enable or disable this mode did bring a lot of discussion within companies.

Using online mode n RDSH environment avoid to carry the OST file in the user’s profile or on a file share but most of the time, user will end up complaining about lag and slowness in Outlook while clicking from a mail to another or reading / answering  email with  more than 10 recipients.

Even with an extreme Outlook tuning, I couldn’t have a super slick user experience as user were used to have before moving to Exchange 365.

One solution was to Enable the Exchange Cached Mode and when asking to Microsoft how we should do, the answer was to put the OST file (Introduction to Outlook Data Files) in the user’s profile because this is the way OST files have been invented, to stay local to the machine where Outlook is. What happen if you have roaming profile ? Basically, you’re screwed and you’re more or less supported by Microsoft, I guess it depend on how many user you have and how much you spend in Microsoft Software Assurance every year. never the less, you can try to play around with Citrix Profile Management to try to Stream the several Gb of data of these OST files, you will end up with a risk of network contention during pick hour connection and disconnection… I won’t speak about your global user profile storage space that will explode and the iOPs generated on the RSDH servers…

Another solution is to bring back Exchange on premise, in the Datacenter. Hybride mode powered, but you need machine again, people to support it again as well.

There are out there, people who understand there was a gap to fill in there and some products are available to address this particular issue. FSLogix™ Office 365 Container for Citrix is a promising solution (still in beta, July 2016)



Then putting these OST files on a network share remain, in the end the best alternative. As these file will be iOPs intensive, a dedicated qtree / storage will be necessary to avoid impacting roaming profiles storage or user’s homedir for example… Atlantis Hyperscale is a great example and what can be done to solve this particular issue.


Good news, there are many ways to fix these issues.. bad news, it cost more and more again…  Whatever you chose Hybrid mode, Software solution , or hardware / storage, it will cost more. In the end, if you add to Exchange 365 cost :

  • Exchange 365 + 3rd party Software to handle OST files + Man days
  • Exchange 365 + Hybrid infrastructure on-premise + Man days
  • Exchange 365 + High Performance Storage = Man days

It looks like almost every time a fucked up old project not being delivered on time with a result who is not the one aim at first, economy…

I hope  this blog gave you some insight what’s going on with Office 365 and RDSH environment and will avoid you to fall into this trap 🙂