How do I migrate more than 20GB of Public Folder data to Office 365?
Office 365 has several hard limits for Public Folders. One limit is that Public Folder mailboxes cannot be larger than 20GB. This means that the folders that are assigned to a given Public Folder mailbox cannot have an aggregate size greater than 20GB. When in normal use, if a Public Folder mailbox gets close to the 20GB 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 20GB. 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 20GB 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 20GB. In order to ensure the aggregate size of all folders in a Public Folder mailbox is below 20GB, 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 20GB limit.
If running a Public Folder migration, and there is more than 20GB 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 20GB limit.
If this is not done, once the 20GB 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 20GB:
- Create a Public Folder migration project.
- Select the Source and enter admin credentials.
- Select the Destination and enter admin credentials.
- Specify the Source path for the project.
- 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 20GB.
- Upon receipt, Support will send you a confirmation.
- 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 20GB 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
- Once the Public Folder mapping script has completed, Support will provide two (2) PowerShell scripts. These will be supplied via the Support ticket system. These must be run by you against the Office 365 environment. Instructions will be included with the scripts. These scripts will complete within a matter of minutes.
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.
- Once complete, the Destination environment will be ready to begin the Public Folder migration.
- Now log in to MigrationWiz, select the Public Folder project that was previously set up. Then follow the steps in the relevant Public Folder Migration Guide; for example, when the Source is On-Premises Exchange, refer to KB005459.