​​How do I migrate more than 50GB of Public Folder data to Office 365?

Answer:​

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Office 365 has several hard limits for Public Folders.  One limit is that Public Folder mailboxes cannot be larger than 50GB. This means that the folders that are assigned to a given Public Folder mailbox cannot have an aggregate size greater than 50GB. When in normal use, if a Public Folder mailbox gets close to the 50GB size limit, Office 365 will detect this and create another Public Folder mailbox, and then run a rebalancing operation in order to keep the aggregate size of all folders in a given mailbox below 50GB. When migrating data, we add items to Public Folders much faster than Office 365 is expecting them. This means that when a Public Folder mailbox gets close to the 50GB limit, Office 365 does not have enough time to run a rebalancing operation to make sure that folders are split across enough Public Folder mailboxes to keep the aggregate size below 50GB. In order to ensure the aggregate size of all folders in a Public Folder mailbox is below 50GB, an operation has to be performed before a migration begins that will properly allocate Public Folders to the correct Public Folder mailboxes in order to allow the mailboxes to stay below the 50GB limit.

If running a Public Folder migration, and there is more than 50GB of data that you are migrating, contact BitTitan Support so that we can generate the PowerShell scripts necessary to properly provision the Public Folder mailboxes, as well as the script necessary to allocate the Public Folders to the correct Public Folder mailboxes to keep the aggregate size below the 50GB limit.

​If this is not done, once the 50GB limit in the primary Public Folder mailbox is reached, it will be necessary to wait for the rebalancing operation (by Microsoft) to complete before continuing the migration, which can take up to two (2) weeks.

Here is the correct sequence of events to follow when performing a Public Folder migration, if the total of the Public Folders is greater than 50GB:

1. Create a Public Folder migration project.
2. Select the Source and enter admin credentials.
3. Select the Destination and enter admin credentials.
4. Specify the Source path for the project.
5. Submit a ticket to Support by following the directions in KB004529. In the ticket description notes, add the name of the Public Folder migration project, and specify that the total of the Public Folders is greater than 50GB.
6. Upon receipt, Support will send you a confirmation.
7. Support will then run scripts that will allocate Public Folders to the correct Public Folder mailboxes in order to allow the mailboxes to stay below the 50GB limit. This can take several days to complete. For example, if the total Public Folder size is greater than 100GB, it will likely take more than two (2) days. This script will query the Source environment to calculate the size of each item, the number of items in each folder, etc. 

• Important:  Any new folders created after the Public Folder split is initiated will not be in scope for the migration. KB005239

• Note: If running Public Folders in hybrid mode, refer to KB005133 prior to running these scripts; the article will explain the required steps to follow in order to be able to run the scripts successfully.