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Think of a normal N-tier application running on a single Windows 2003 Small Business Server.  You likely have multiple servers/services providing support for the web application via ISA, Exchange, SQL Server, IIS, Active Directory, etc., all running on the same physical box.

Now think of the common bottlenecks in this situation: w3wp.exe (IIS App Pool worker processes) stopping, Exchange store corruption, SQL server latency, Disk I/O latency, etc.

For a web host, using virtualization to segregate these different tiers can be essential to a secure and fault tolerant infrastructure.

First, let’s examine the benefits of segregating the WFE’s (IIS) from the rest of the group.  Having a WFE on a virtual server allows you to quickly recover from most disasters/compromises, quickly scale or downsize your farm, and above all, you can now efficiently reduce the total physical resources required to serve sites/services.

By having a master image, preloaded with required 3rd part applications, components, services, and disk configurations, you can greatly reduce the amount of time it takes to produce new front end webservers.  Some may say that a disk image will give you the same benefit, but with virtualization, you’re also able to dynamically adjust network settings and RAM amounts. In addition, adding disks/SAN resources to the server is extremely simplified compared to having to manually configure and match a RAID configuration to a disk image.

Having multiple virtual front ends also enables you to more efficiently use your centralized storage. Instead of leaving wasted space on a physical server’s hard drives/array, you are now able to reduce the HDD footprint of the VM’s OS partition, and eliminate the need for replication or wasted space on unused physical disks.

Security is also enhanced when you separate the WFE from the SQL store.  Having the SQL farm outside your DMZ not only contributes to a more secure environment, it also reduces the amount of disaster recovery time required in the event if a server rebuild.