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Merging Office 365 Tenants over President’s Day Weekend: The story of 15K mailboxes and 539GB an hour! 

9 Mar 2020 by Mike Weaver

merging office 365 tenants over President's Day weekend

For most, President’s Day weekend is a time to take a break and relax, but this year the Quadrotech team was busy merging Office 365 on behalf of a client.

15,000 mailboxes aren’t typically problematic, as users can be grouped and waved over the course of several weeks or months. However, this particular Office 365 tenant to tenant migration presented several challenges that required special treatment.

Migrating users by department (Sales, Marketing, Finance, etc.) is rarely a good idea, as most organizations naturally have a high level of cross-departmental collaboration; such a basic migration strategy would see workgroups split up and unable to communicate for a prolonged period.

Merging Office 365 tenants with a tailored approach

For small migrations over a short period, the consequences of splitting groups won’t be a major issue in the grand scheme of things, as the project will be over in a timely fashion. However, for big migrations with planned batches spanning several months, this might mean being incommunicado for half-a-year or more, which is obviously unacceptable.

Accurately identifying workgroups is a daunting challenge for most, one that would usually require knowledge of organizational operations and a deep study of SQL or Excel data (while downing several cups of coffee).  Essentially, you need to write your own scripts and beg for someone with access to run it.

However, the analytics feature of Nova – our comprehensive Office 365 management software – meant collecting this data was made easy. Yet, for some companies, grouping (or batching) users is still difficult.

The client we were working with here had very high cross-departmental coworking, so they couldn’t contemplate moving users in multiple batches. After reviewing the data, we agreed to perform an ambitious ‘big bang’ and cutover during the President’s Day weekend – a ‘quietish’ period that allowed additional time before staff returned to their desks.

Migrations as a Service

For a successful project, both pre-sync and cutover had to be sufficiently monitored and expertly executed, which is where our skilled Ops Team came in, armed with our powerful Office 365 to Office 365 migration tool, Cloud Commander.

With the client’s dedicated focus, our experienced project management, and excellent collaboration with Microsoft’s support team, we delivered a very successful result. The uniquely adaptable architecture of our software meant we were able to set a new hourly migration record, clocking a top speed of 539.11 GB in just one hour.

539GB per hour when merging Office 365 tenants

This was an incredible milestone for us, but high-performance levels weren’t a flash-in-the-pan spike; we sustained 128 hours at 400 GB+ per hour, with 43 hours of 500 GB+ per hour during pre-sync.

We may have gone on to record even more success, but we simply moved all the data ahead of schedule.

The business results

The throughput of our software allowed the migration to stay ahead of time with 98% of users moving within the allotted maintenance window, despite a considerable domain ejection delay.

15k users in one weekend, with almost all of them having 100% of their data moved during the window. All on a fixed price, fixed outcome deal.

High-performance software and expert ops are a great match for high-performing clients, combining to create the perfect conditions to break records.

Fun fact: President’s Day weekend is known for having the best sales on mattresses and, after such a fast-paced project, it’s fair to say we all needed a lay down come Monday afternoon.

To learn more about merging Office 365 tenants, please contact us today.


Mike Weaver

Mike Weaver is the Product Owner of Cloud Commander, PST Flight Deck and Mailbox Shuttle. Bringing a wealth of experience in large Enterprise Environments, Mike assists with complex, multi-product implementations of all Quadrotech solutions. Prior to joining Quadrotech, Mike led Merger, Acquisition, and Divesture Messaging Projects. He also administered, and engineered solutions for Microsoft Exchange, Veritas Enterprise Vault, PST Flight Deck, Archive Shuttle, as well as many other solutions and products in the Windows Infrastructure space. Mike holds a Master of Business Administration from Quinnipiac University, and a Bachelor of Science from Central Connecticut State University.