300 users.
With VDI, I take the same piece of hardware. I run a hypervisor on it and then create
lots of virtual machines, and each virtual machine runs a full client operating system
(which has CPU and memory requirements). Then I run the applications on that client
OS. Hypervisors have some great memory technologies to get the most from the box,
assigning memory only as the OS needs it. Typically, a client OS will need around
700MB of memory just to log on, and then additional memory as applications run, so
let’s say a very low 1GB of memory per virtual machine. Remember that realistically
the actual memory needed could rise to 2GB. On that same server, removing memory
for the OS, that may be 62 virtual machines.
On the same server, with session virtualization, I get five times more users than with
VDI, and in some environments I see ten times more users on a session-based
environment than the same VDI environment. That’s a huge difference in bang for the
buck for the same hardware. There are other differences that also make VDI more
expensive.
The licensing is also different because with session virtualization, an RDS Client
Access License is required, but with VDI numerous licenses are needed, depending on
the exact solution.
So the issue is not that session virtualization has capabilities beyond VDI, but rather
that VDI is more expensive, requires more hardware, and needs more management
than session virtualization. This means, where possible, use more session
virtualization and save VDI for where it’s actually needed.
I’ve heard of organizations talking about moving to VDI to save money. I’ve never
found this to be the case. If an organization has a poorly managed desktop
environment, moving it to the datacenter with VDI will mean a poorly managed VDI
and a bigger mess. The move to VDI normally introduces a whole new infrastructure
that makes the environment more managed, which in reality could have been used to
clean up the physical desktop environment without purchasing all of the hardware for
the VDI servers.
What is interesting is when I talk to clients who need to enable BYOD scenarios or
overseas contractors, they always talk VDI; they never think of session virtualization.
The reason is simply that there are some companies that have only VDI solutions and
don’t have a session virtualization solution. Therefore, VDI is the solution for
everything. If you sell only hammers, then a hammer is the right tool for everything.
Take time to understand your requirements and identify the right solution based on
the factors I’ve discussed. To summarize, start with a normal desktop operating
system that is well managed. If that is not an option, think session virtualization. If
session virtualization is not an option because the users are power users, the users are
developers, or the applications will not run on a server OS or run multiple instances
on one OS, then use VDI. Remember, you don’t have to pick one solution. Use a well-
managed desktop environment for corporate assets that can run a modern desktop OS,