Strategies for Successful Cloud-to-Cloud Migrations: When Coexistence Makes Sense

Guest Post

According to Bitglass, a leading Cloud Access Security Broker, use of Microsoft Office 365 globally grew from 34 percent in 2016 to 56 percent in 2018.

This is a clear indication that a large and growing number of organizations are relying on the cloud for workplace productivity. It also validates a trend we’re seeing at BitTitan: the increase in cloud-to-cloud migrations.

Often a merger, acquisition or divestiture is the impetus for moving from one cloud to another. There’s a need to bring an entire company or business unit into another company’s environment. If both utilize Office 365, this calls for a tenant-to-tenant (T2T) migration.

The T2T migration involves moving mailboxes, OneDrive or SharePoint instances, personal archives or Personal Storage Tables (PSTs), and other data associated with various cloud applications from one Office 365 tenant to another. They are often time-consuming, high-stakes projects.

Fortunately, steps can be taken to minimize the risk of problems and make the process smoother for all involved.

To Coexist or Not

The goal of any migration is a seamless transition that preserves business continuity through the change. It used to be that IT admins would move everyone at once over the weekend or at another time that wouldn’t be disruptive. Today, however, with so many organizations doing business globally or allowing mobile and remote workers to log in any time day or night, there are often no good times to launch a migration.

Kris Harness, founder and president with KDH Consulting agrees. “The old model of shutting things down on Friday night, migrating over the weekend and reopening for business on Monday morning is seldom an option,” says Harness. “Increasingly, we need to take a staged approach where groups of users or departments are migrated in phases at separate times.”

While this staged approach works well for IT teams who want to avoid disrupting business operations, the drawback is that some users within the organization remain on the source while others have migrated to the new destination, creating major communication problems. That’s where coexistence  is essential in ensuring a seamless migration.

There is also the option of combining coexistence with selective migration of older, archived or less-essential items. This can shorten the time window required for the most critical parts of the migration. Typical scenarios include pre-migrating items older than 90 days, or migrating only the most recent 60 days of email and backfilling the rest of the mailboxes and data after the fact.

By enabling coexistence between two Office 365 tenants throughout the migration, the IT team eliminates end-user disruption throughout the entire process, and has greater flexibility over when and how to accomplish the transition.

How Coexistence Works

Coexistence seamlessly handles the two biggest problems that IT managers face. Throughout migration, it ensures emails are routed to the correct inbox, and maintains constant visibility to the free/busy information in users’ calendars.

To implement coexistence, the process is simple.

First, enable organizational sharing on the Office 365 tenants. Create mail-enabled contacts with an external address that resolves back to the source mailbox, so the unmigrated users have a mailbox on the source and a mail-enabled contact on the destination.

As each user’s data is migrated, remove the mail-enabled contact from the destination and create an Office 365-licensed user account. This creates the mailbox so you can migrate the mail items into it. Since the user remains on the source, there is still a forward from the destination back to the source.

When the migration is completed, the mailbox on the source can be removed (replaced with a mail-enabled contact, with an external address of the destination mailbox) or a kept in place with a forward to the new destination mailbox. Now the user needs to reconfigure their devices to the new destination Office 365 mailbox.

Domain Name: Same or Different?

The critical factor that allows coexistence is whether the Source and Destination domains are the same or different.

If they’re different — as is most often the case with a merger, acquisition or divestiture — then a staged migration with coexistence as outlined above is a great option.

If they’re the same, then coexistence can’t happen, because Microsoft stipulates that a domain name can only exist on one tenant at a time. Admins who want to perform a T2T migration and use the same domain name are essentially limited to a cutover-style migration.

The key to success with any migration is careful preplanning. Beforehand, select the strategy that will work for you: a cutover, or a staged approach (with or without coexistence). Next, map out the entire migration process and make sure the timelines are realistic. Once you begin the migration, be sure that required technical resources are on hand and communicate clearly with end users. This should ensure that your migration will be  smooth.

Kelsey Epps is a senior technical partner strategist with BitTitan. A 20-year IT industry veteran, Kelsey works with MSPs and IT specialists on the technical preplanning aspects of the most complex migrations projects.


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