The key characteristics of the data that is stored by a directory service correspond to size and latency. Active Directory should store objects that are not so large that they hamper replication and not so unstable that they change before an update replicates to all replicas in the forest. Therefore, large, unstructured data sets and data values that change frequently are not appropriate for storage in Active Directory.
In general, Active Directory is appropriate for the storage of data that has the following characteristics:
The data is globally useful information in the domain that needs to be replicated to each Active Directory domain controller.
The data has well-defined object attributes and semantics.
The data has a useful life that is at least two times the maximum replication latency for the forest (to include replication of data that is marked to replicate to the global catalog). In general, if data can become outdated before the completion of a replication cycle or shortly thereafter, it should not be stored in Active Directory. Clients should be able to tolerate the inability to update data for at least as long as it takes for the data to be replicated throughout the domain.
The data-per-attribute value is not so large that it affects performance. An attribute value is replicated as a single block of data; therefore, an attribute that is x megabytes in size requires an equivalent amount of buffer space in the sending and in the receiving domain controllers. If the amount of required buffer space is large, the performance of the domain controller can be adversely affected.