WHAT IS FSMO ROLES IN ACTIVE DIRECTORY

Flexible single master operation (FSMO) is a Microsoft Active Directory feature that is a specialized domain controller task used when standard data transfer and update methods are inadequate. Tasks that do not suit multimaster replication are only viable as flexible single-master operations.

Multimaster models have a number of operators, which are held by a single master. This problem is solved by applying a number of operations to a single domain controller. A single domain controller holds the role for a particular operation and is the single master for that operation. These operation masters are called flexible single-master operations. - (Source)

For more information, please go through Microsoft' KB on FSMO Multi-Master and Single Master Roles. (Source)

ROLES OF ACTIVE DIRECTORY

1. Transfer of Roles
2. Seize of Roles

TRANSFER OF ROLES

We recommend that you transfer FSMO roles in the following scenarios:

• The current role holder is operational and can be accessed on the network by the new FSMO owner.
• You are gracefully demoting a domain controller that currently owns FSMO roles that you want to assign to a specific domain controller in your Active Directory forest.
• The domain controller that currently owns FSMO roles is being taken offline for scheduled maintenance and you need specific FSMO roles to be assigned to a “live” domain controller. This may be required to perform operations that connect to the FSMO owner. This would be especially true for the PDC Emulator role but less true for the RID master role, the Domain naming master role and the Schema master roles.