Database server as secondary domain controller - acceptable?
We currently have an SBS 2003 box as our primary domain controller (also running Exchange and file shares). We also have two Windows 2003 Standard R2 servers on the network: one runs Oracle 10g and holds a database used by about 9 people; the other runs MS SQL 2005 and hosts our Microsoft Dynamics CRM database, accessed frequently by about 12 people and infrequently by another 15 or so..
I would really like to add a secondary domain controller to the network for fault tolerance reasons. Would it be acceptable to make one of the database machines a secondary domain controller? Would I expect to see much of a performance impact? I am under the impression that, in an organization as small as ours (approx 55 users) that the DC-related activity on a server would be extremely small.
Can someone please tell me if I am correct in my thinking, and provide any recommendations?