Beginning with version 5.02 of Sharegate, you can now migrate site collections and promote sites and sub-sites to top-level sites or a site collections.
Promote a site to a site collection
- Use the Copy Site Objects feature
- Connect to your source central administration or directly to your site
- Connect to your destination central administration
- On the source side, select the site you want to promote and drag and drop it to the destination (you must be at the site collection level on the destination side).
5. Configure the migration options:
- Keep or change the site collection title
- Select the URL
- Assign a Quota Template
- Select what to include during the migration (content, permissions ...)
The options pop-up window will differ depending your SharePoint version (On-Prem or O365), please read more information here.
6. During the copy process, you should see the Creating Site Collection status.
Promote a subsite to a top-level site
The process is exactly the same as promoting a site to a site collection. The only difference being the need to drill down to your destination location in the right-side navigation panel instead of staying at the site collection level.
When migrating content to Office 365, a special pipeline is offered by Microsoft that can significantly increase migration speeds. You first have to configure the Performance Options.