I recently discovered a small bump in the road when it comes to upgrading an excisting Lync 2010 Enterprise pool to Lync 2013 Enterprise.
The SQL server instance not only has to be unique to the Lync 2013 Enterprise Pool, but it also has to be on a dedicated SQL server not already in use by the Lync 2010 Pool.
This means, when upgrading from Lync 2010 Enterprise to Lync 2013 Enterprise, take into concideration that you would need a new SQL server as well.
The Microsoft documentation on the subject is not very easy to find(unless you search specifically for SQL migration scenarios), and even in this article http://technet.microsoft.com/en-us/library/gg425764.aspx it’s not clear that the requirement for a new SQL server is only for an Enterprise scenario.
A possible workaround(in a small organization) could be to install Lync 2013 Standard Edition, migrate users and move the CMS, then reinstall Lync 2010 Enterprise server as Lync 2013 Enterprise pointing towards the old SQL server and then move everything back…
Your Call 🙂