Placing physical machines in separate sites protects against loss in local disasters.
Follow these Private and Sync Link requirements:

• NICs, fiber converters, and switches in the private network must be non-routed, non-blocking, dedicated, and provide 100MB (Private only) and 1000MB transfer rates.
• Roundtrip latency must not exceed 10 ms. Calculate latency at 1 ms for each 100 miles of fiber, and less than 1 ms for each non-routed, non-blocking switch.
• No general business or management traffic.

Also see Split-Site considerations in Avance Network Requirements.