Windows network load-balancing vs. hardware load-balancing
Windows network load balancing (NLB) is an easy choice if money is an issue and your organization doesn't plan on installing the CAS role with a Mailbox role as part of a DAG. (Apparently there is a problem combining the Windows NLB services with the Windows Failover Clustering services.) However, if you have more than eight CAS nodes and/or plan to perform multirole CAS-Mailbox installations with DAG, you should consider a hardware load balancer.
You might think a hardware load balancer is a big expense that's not likely in your budget, but check those numbers again. Ideally, you'd account for your high-availability and load-balancing requirements up front, so the need for a hardware load balancer doesn't come as a surprise.
If you're looking for a hardware load balancer, you might consider Kemp Technologies, which has a solid reputation and reasonably priced load balancers. For smaller IT shops, Kemp has a $2,000 load balancer; for larger shops, its lineup includes virtualized servers rather than physical rack systems.
Hypervisor-based load-balancing servers
Another approach is to use virtualized load balancers rather than physical appliances. It's obviously going to be a cheaper because you don't need dedicated storage hardware. They provide the flexibility you need for CAS balancing and other load balancing for systems such as SharePoint and Office Communication Server/Lync Server.
Kemp's Virtual LoadMaster works with both Hyper-V and VMware, with prices starting at $1,500. It uses the same software as the company's hardware load balancer, so it provides the same features such as L4 load balancing, L7 content switching, and SSL off-loading.
Get your Exchange servers balanced and available
Your key concern is to ensure you have redundancy and can provide disk, server, and site resiliency in your Exchange environment. Typically, Exchange admins focus on the Mailbox server role for such tasks. Without the Hub Transport and CAS server roles, your Exchange environment is dead in the water.
Luckily, the Hub Transport role magically load balances and is redundant the moment you install a second one. No such luck with the CAS server -- but now you know how to address that.
This article, "Exchange 2010: The secret to staying afloat when disaster strikes," was originally published at InfoWorld.com. Read more of J. Peter Bruzzese's Enterprise Windows blog and follow the latest developments in business software and Windows at InfoWorld.com.