Issue

There are several ways to migrate Syensqo users and data towards the Microsoft environment, all have technical complexities and user impacts.
Syensqo is too large to consider a “big bang” approach while ensuring low disruption, and a migration by wave will create a coexistence period of 3 to 5 weeks (when both Google Workspace and Microsoft 365 will be used simultaneously).
Prolonged coexistence can lead to increased complexity, higher support costs, user confusion, and potential security risks.

Therefore, it is critical to identify a migration approach that minimizes the duration of dual-platform usage while ensuring a smooth transition, business continuity, and minimal disruption to employees.
The decision to be made is to select the most effective migration strategy that reduces the coexistence period, addresses technical and operational requirements, and supports user experience.

Recommendation

It is recommended that Syensqo adopts a wave-based migration approach with organizational allotment (by GBU / Function) rather than a "big bang" migration.

Benefits of a Wave-Based Approach

• Controlled Transition: Migrating users and data in defined waves allows for better management of technical and operational complexities.
• Risk Mitigation: Issues can be identified and resolved early in smaller groups, reducing the risk of widespread disruption.
• User Support: IT and support teams can focus on smaller user groups at a time, providing more effective training and troubleshooting.
• Business Continuity: Critical business functions can be prioritized and migrated at optimal times, minimizing impact on day-to-day operations.
• Reduced Coexistence Period: While not as immediate as a big bang, a well-planned wave approach can still significantly shorten the coexistence period by enabling parallel preparation and execution.

Background & Context

The migration process with Microsoft Fast Track happens with a Pre-Staging phase, where historical user data is pre-loaded, and a "sync event" where the delta is synchronized before performing the cutover.
Users are able to work throughout the pre-staging phase but once the sync event is launched, any modification of existing files or emails would not be reflected in the target environment. 

A big bang scenario is ruled out because the pre-staging phase for all Syensqo users would take about 3 months, which endangers the timeline, and more importantly because the sync event would span over approximately 8 days which would highly disturb business continuity.

By following this strategy, the organization aims to achieve the following:

• Enhance collaboration and productivity by consolidating services under Microsoft 365.
• Ensure data integrity and compliance with enterprise standards.
• Minimize risks and downtime during the migration process.

Assumptions

N/A

Constraints

• Avanade, in collaboration with Microsoft Fast track, shares that a reasonable threshold of #users per wave is 4000 (for migration performance and post-migration service quality)
• Business disruption / freeze of the collaboration on a weekday cannot be tolerated as it would have direct and significant impacts on business activities

Impacts

• A wave migration approach results in a “coexistence period” of up to 5 weeks, during which some employees will have moved to M365 while others will remain on the GWS environment.

• This 3 to 5 weeks period will introduce complexities in the way employees consult calendar availability of their non-migrated peers, and book meeting rooms.

Here is a visual way of presenting this coexistence period:

Options considered

Option 1:  One Shot Cutover (ruled out)

Option 2A: Migration by waves - GBU/BSA/GBS driven

Focused on enabling intra-GBU collaboration, avoiding coexistence use cases between employees of a same GBU. 

Business Representatives have preferred this option over Option 2B, with 13 votes out of 15 (votes performed on November 25th 2025 during the "GBU Connection" call)

Avanade has created an initial proposition of the order and grouping of the GBU’s in 4 actual Users/GBU waves and 1 final wave with users that cannot be attached to a GBU and the Shared Mailboxes.

We will further align on the best combination and order of the GBU waves taking into account the above guidelines.

Option 2B: Migration by waves - regional approach driven

With this construct of waves based on region, we primarily focus on aligning the migrated people on time zone’s

One of the key reasons for this approach lies in meeting room and calendar functionality. Once a user is migrated to Microsoft 365, their mailbox and calendar no longer reside in Google Workspace. From that moment onward:

• • They must book and use meeting rooms that are now hosted in Microsoft Exchange Online.
  • Any meeting rooms remaining in Google Workspace will no longer be accessible or reliable for migrated users.
  • If users from the same physical office location or country are split across platforms (e.g., HR and IT are migrated but Finance is not), it creates confusion and technical issues with room bookings, calendar invites, and shared availability.

Therefore, to maintain calendar integrity and ensure reliable resource booking, we migrate complete countries together.

Evaluation

	Option 1 One Shot Cut Over	Option 2A Migration by waves - GBU/BSA/GBS driven	Option 2B Migration by waves - regional approach driven
Technical Feasibility	16 K active users (20 K active Mailboxes ~229 TB mailbox + ~181 TB MyDrive) 3194 active shared drives (~ 63,6 TB Shared Drives)+ 2116 AODocs Lib. (13,7 TB)	More controlled and iterative approach, in line with the migration's partner strong recommendation.	More controlled and iterative approach, in line with the migration's partner strong recommendation. Simpler meeting room hardware switch (all meeting rooms in the related site will be switched) Higher risk of miss-assignment as geographical attachment might be less precise than organizational information in the IT systems (i.e. migrating a user that is not actually located in the targeted region/site for this wave).
User Impact	All of Syensqo is impacted at the same time "band aid" approach in some cases can be seen as a better approach to change management Show stopper: 8 days of disruption for the sync event before cutover	Smoother Intra-GBU collaboration as everyone will have Teams Chat, Outlook emails & calendar, and access to OneDrive for simple file sharing Cross-GBU collaboration impacted during coexistence: (Calendar availability, Room Booking) Complex Meeting rooms management for sites that have mixed GBU presence (ex: meeting rooms might have to be booked from migrated-users’ agendas only)	No coexistence issues within a single site, especially beneficial for sites with mixed GBU presence Easier planification of meeting rooms hardware configuration and booking by users during migration Cross-region travels during the coexistence will require more careful planification (ex: local contact for room booking)
Support Impact	Very complex to handle a company-wide, international major change, with important user impacts	Ramp up of full support through a controlled process Worldwide population in a single wave is more challenging for of IT support and project team around cutover Will be supporting the users in a same country on two different platforms	Ramp up of full support through a controlled process Heavy load on a given time zone/region for each wave
Operational Complexity	N/A	N/A	N/A
GBU/BSA/GBS Feedback	N/A	13/15 votes for this scenario	2/15 votes for this scenario
Cost	N/A - Fast Track included in the Microsoft Contract

See also

The following section describes relevant documentation: