Understanding Permissions and the SharePoint Migration Tool

The SharePoint Migration Tool permission control is effected by various conditions. The following table lists all the conditions and the corresponding results.

Source Preserve user permissions set to ON Are you migrating to the Target library root folder or sub folder? Target library permission before migration Target library permission after migration Note
File share No Root folder Inherited Inherited Role assignments of the target library and existing files won't be changed; migrated files have Inherited permission (Inherited role assignments from target library)
File share No Root folder Unique Unique Role assignments of the target library and existing files won't be changed; migrated files have Inherited permission (Inherited role assignments from target library)
File share No Sub folder Inherited Inherited Role assignments of the target library and existing files won't be changed; migrated files have Inherited permission (Inherited role assignments from target library)
File share No Sub folder Unique Unique Role assignments of the target library and existing files won't be changed; migrated files have Inherited permission (Inherited role assignments from target library)
File share Yes Root folder Inherited Unique Role assignments of the target library will be replaced by that in source root folder. Existing files with inherited permissions will still be inherited permission but with a new role assignment from target library. Existing files with Unique permissions won't be changed. Migrated files without any permission in the source will have inherited permissions and inherited role assignments from the target library. Migrated files with any permissions in the source will carry over these permissions as unique.
File share Yes Root folder Unique Unique Permissions from the source folder will be added as new role assignments to the target library. Existing files with inherited permissions will still be inherited permissions but with a new role assignment from the target library. Existing files with unique permissions won't be changed. Migrated files without any permissions in the source will have inherited permissions and inherited role assignments from the target library. Migrated files with any permissions in the source will carry over these permissions as Unique.
File share Yes Sub folder Inherited Inherited Role assignments of the target library and existing files won't be changed. Permissions from source folder and files will be carried over to the target subfolder and corresponding files, which will have Unique permissions as new role assignments.
File share Yes Sub folder Unique Unique Role assignments of the target library and existing files won't be changed. Permissions from source folder and files will be carried over to the target subfolder and corresponding files which will have Unique permission as new role assignments.
List/Document library No Root folder Inherited Inherited Same as File share migration with same condition
List/Document library No Root folder Unique Unique Same as File share migration with same condition
Document library No Sub folder Inherited Inherited Same as File share migration with same condition
Document library No Sub folder Unique Unique Same as File share migration with same condition
List/Document library Yes Root folder Inherited Unique Same as File share migration with same condition
list/Document library Yes Root folder Unique Unique Same as File share migration with same condition
Document library Yes Sub folder Inherited Inherited Same as File share migration with same condition
Document library Yes Sub folder Unique Unique Same as File share migration with same condition
Site/Web No NA Inherited Inherited Role assignment of target site/web will be unchanged
Site/Web No NA Unique Unique Role assignment of target site/web will be unchanged
Site/Web Yes NA Inherited  Unique Role assignment of target site/web will be replaced by those in the source site/web
Site/Web(A) with Subsite B (both migrated with SPMT) Yes NA Subsite B or sub web inherited from main Site A Subsite B/web unique from the new SPO main site A Site A is migrated as described for normal site migration. Subsite B becomes unique and role assignment will be replaced by those in the source Subsite B
Site/Web Yes NA Unique Unique Role assignment of source site/web will be added as new role assignments to the target site/web