How many TCP connections are formed with SNAT and without SNAT ?

This is not as simple a question as it seems. I'll try to break it down.

Essentially, the use of SNAT does not make a difference to the number of TCP connections in use. What does affect the number of TCP connections are two things - the virtual server type and OneConnect.

A Performance Layer 4 or forwarding virtual server does not interrupt the TCP protocol - it is a single TCP connection on the client and server side. A Standard Virtual Server with a TCP profile attached will create a client-side TCP connection and a completely different server-side TCP connection. With SNAT assigned, the source address will be the SNAT address. Without SNAT, the source address will be the client address. Other than that, no difference.

When a OneConnect profile is assigned to a standard virtual server, a pool of serverside TCP connections is used to multiplex the client side connections. So there could be a million client-side connections and a thousand server side connections.