Maximum supports up to 75 users/devices
Should be installed as a DC
Can’t be more than one DC in the same network
Since single DC on a single hardware, can’t have secondary domain
Since SBS 2003 R2 is designed for small networks 5-75 users/device. SBS is best suited for small business where the network is peer to peer.
You can’t do load balancing or cluster using a SBS 2003 R2 since these features do not come under a small business network. A small business network is mostly a few numbers of PCs (5-75) without a server.
Since the SBS 2003 R2 is for small business network where the business data is not used for online transaction or if there is a downtime it wouldn’t affect the business. So SBS 2003 R2 there is no need to have the features such as such as clustering and load balancing and you can’t have another DC in the same SBS 2003 R2 DC.