Reecently, I’ve been asked by a number of clients to help size and implement Citrix NetScaler VPX virtual appliances. Citrix positions the NetScaler as a ‘high-speed load balancing and content switching, data compression, content cashing, SSL acceleration, network optimization, application visibility and application security’ platform. With so many available functions, firms need to size carefully which VPX model is right for them. The VPX is sold in 200, 1000, and 3000 Mbps virtual appliance models.
Typically I’ve seen firms start small and grow to leverage more of their NetScalers’ functions over time. A firm might replace its Secure Gateways with virtual Access Gateways running on the VPX, with the intention of adding load balanced Exchange 2010 traffic to the VPX down the road.
If you find yourself in a similar situation, you can use some basic calculations to choose the right VPX, or MPX, based on some of the most common traffic types. Also note that it’s easy to purchase a small model and upgrade later if your bandwidth requirements change. Many firms overestimate their needs, even choosing physical MPX-level NetScalers when all they need is a virtual VPX.
The key factors in choosing between the MPX and VPX are bandwidth and processing power. The physical MPX has the clear advantage in processing power, which is crucial for firms with high user counts. For firms that need to serve a sufficiently high number of concurrent users, we recommend the MPX, both for daily remote access use and for backup data centers DR access. Underestimating capacity needs in a backup data center is a common mistake. Many firms view equipping a backup data center as a chance to save money, and opt for the lower-bandwidth VPX. This makes sense if you plan for day-to-day bandwidth needs, but fails to consider how bandwidth needs will expand in the event of a failover. Backup equipment is meant to be used for emergencies, not daily production, so it makes sense to size for former instead of the latter.
For a copy of the quick-and-dirty Excel spreadsheet I’ve created for calculating bandwidth needs, feel free to contact me at: Spreadsheet Request. The spreadsheet includes calculations for the following products bandwidth usage when leveraging a NetScaler for load balancing:
- Outlook Anywhere Cache Mode
- Outlook Anywhere Online Mode
- Outlook Web App w/ Exchange 2010 SP1 or SP2
- Outlook Web App pre Exchange 2010 SP1
- SSL VPN