What Happens During SchemaPrep in Lync Server 2010?

Lync Server 2010, just like previous versions of OCS, has new Active Directory schema that needs to be loaded before you can install any server roles.  In Lync Server 2010 the new schema is split up into four different files: 

  • BackCompatSchema.ldf
  • ExternalSchema.ldf
  • ServerSchema.ldf
  • VersionSchema.ldf

These files can be found on the installation media in \Support\Schema.  Running the SchemaPrep step as part of the install will automatically import the changes contained in these files into Active Directory.  If you would like to manually import the schema into Active Directory, via ldifde, you need to make sure to apply the schema in a specific order:

  1. ExternalSchema.ldf
  2. ServerSchema.ldf
  3. BackCompatSchema.ldf
  4. VersionSchema.ldf

Remember that no matter whether if you are migrating from a previous version of OCS or installing Lync Server 2010 in a greenfield environment, you need to apply all four schema files.

The following are the new attributes that are added to your Active Directory schema during SchemaPrep:

Attribute Description


Unique identifier of the tenant. This should be unique across all tenants.


This attribute is used to store name value pairs.


Urn of the owner for the application contact.


This attribute is used to store name value pairs for target policies on OCS user.


This attribute used in split domain topology and contains an Fqdn.


This attribute contains Device ID of the Private Line Device.


The xml blob contains audio conferencing provider information for a user.


Unique identifier of a group.  Used to group address book entries




The ExternalSchema.ldf file contains two changes.  It changes the thumbnailphoto attribute to replicate to the global catalog for the address book service.  It also adds the ms-Exch-UC-Voice-Mail-Settings attribute to AD. 


The ServerSchema.ldf file contains most of the attribute changes for Lync Server 2010. 


This schema file contains all the previous attributes for OCS 2007 R2.  This is mainly used in a greenfield deployment where the RTC attributes don't already exist.


The VersionSchema.ldf file is the last file to be run.  All this schema file does is to set the ms-RTC-SIP-SchemaVersion attribute to the Lync Server 2010 version (1100).