The Pros and Cons of Virtual Desktop Infrastructure

This article weighing the pros and cons of VDI is making the rounds on the blogoshphere right now.  Here’s my quick take.

The idea with VDI is that instead of users using applications on a Terminal Server or their PC they run an RDP or ICA session that connects to a virtual machine running Vista or Windows 7 on a server in the data centre.  The server will run many desktop virtual machines and users connect to them via a broker service.  The broker deploys the VM’s on behalf of the user/administrators from a golden sysprepped image(s).  There can be a pool of shared and/or dedicated per user VM’s depending on policy.

The PC?

The power of the PC is that the end user computing environment is on the user’s desk.  The weakness of the PC is that the end user computing environment is on the user’s desk.  Some one has to build it, patch it, put updates on it, software on it, secure it, etc.  We can automate lots of that, if not all of that.  But most organisations have failed to do that well despite the available tools out there.  The biggest problem is that the data the user is working on is often far away from the user and their PC. 

Back in the 90’s we learned about Thin Client computing.  Why change the PC every 3 years?  There’s an OS, the hardware, etc, to repurchase and deploy.  There’s helpdesk staff to send out to take care of lots of stuff.  Policies regarding security and data storage locations must be enforced somehow.  We were told that transferring the computing environment to the data centre via Terminal Services (or Citrix)

Why Not Terminal Services?

  • Very prone to issues, e.g. applications are designed for single user machines.  Low level failures can crash the server for everyone.  Memory or processor inefficient applications can reduce the user count per server.
  • Change is slow, e.g. fixing a simple thing for a help desk engineer can become a change control issue taking weeks to complete.  Users used to PC’s won’t accept that.
  • Incompatible applications can create application silos.  App-V can resolve that but that massively increases license costs, e.g. software assurance and you per user MDOP purchase.

I’m not totally slating Terminal Services.  Certainly not.  For bog standard or clean applications, it’s a fine solution especially now with EasyPrint, TS Gateway and RemoteApp.

Why VDI?

VDI takes the best of the PC and puts it with the best of Terminal Services.  Each user gets their own computing environment running a desktop OS.  That’s a familiar computing environment for the user and pretty much most applications should be OK with that.  The desktop OS is running on a server running a virtualisation solution in the data centre.  That centralises the user computing environment beside their server applications and data.  It also reduces the footprint out on the floor so it should reduce helpdesk movement out there.

Sound like it’s going to reduce costs?  I’m not so sure.

Why Not VDI?

Let’s dispel some myths.  Most helpdesk calls are not PC hardware related.  They’re vastly in the minority.  It’s usually applications, printers, phones, Q&A stuff that keeps the phones buzzing.  With PC’s, we can minimise foot traffic by using things like Active Directory Group Policy, Remote Assistance, etc.  Moving the user to a data centre located virtual machine doesn’t remove these calls.  In fact, the same solutions will be used to fix the issues.  Heck, we’ve added further complexity such as bandwidth and the broker to break.

What about VDI being a cheaper solution?  A 2GB RAM HP PC’s with a copy of Vista Business is €362 in Ireland.  It’s got 320GB of disk but we really only need 100GB of that for the desktop OS and applications.  All user specific data will be stored on the network using redirected folders.

What about VDI?  I’m going low end here.  We’ll run a standalone host to keep costs down.  Using a clustered solution will require a SAN of some kind.  We’ll go with a DL385 G6 costing €4880.  We’ll have to add some equipment to it to maximise it’s potential.  We’ll put in 2 RAID 1 drives for the host OS and 14 300GB drives for the VM’s.  The OS drives total €500.  The VM drive total €6650 giving us 3900GB of storage.  That’ll round out as 35VM’s.  For virtualisation, let’s use a free one with RAM oversubscription.  We’ll need another 16GB of RAM to give us a total of 32GB RAM, costing €520.  The second processor works out at €1000.

So here’s the cost comparison for hardware:

  • 35 PC’s = €12,670
  • 35 VM’s = €13,550

I’ve not accounted for monitors, keyboards and mice in this – you need them in both solutions.

We went low end with the VDI host.  If it experiences a hardware issue then 35 users will be unable to work.  You’re likely going to need to build a cluster to protect against that.  That means buying SAN storage and an additional server.  We’re probably doubling the costs of the solution, if not more, by doing that.  You’ve also completely centralised the user computing environment so there will be greater reliance on networking, requiring an upgrade there. 

I also forgot about the OS costs.  Most businesses in Ireland use the OEM OS so there no extra costs there.  But VDI requires leasing a VECD license (to be renamed) every month from MS so there’s additional licensing costs there.  You’re also likely to purchase a broker solution from someone like Citrix or Provision Networks.

But what about all the management savings?  If you need to deploy software, updates, patches, AV, etc to a PC then you need to do the same with a VM.  Sure it’s centralised but you still need all those management applications to do the work.  And you’re still likely to need 1 helpdesk admin for every 50 users to take care of all that support.

Oh – you’ll still need something for VDI on the end user’s desktop.  I already discounted monitors from the equation.  But you still need a terminal of some kind in VDI on the desktop.  That could be a recycled PC.  Or it could be a terminal, costing from €203 per machine.  They also need to be managed and upgraded in someway too.

Which Way To Go?

VDI does have a place but I’d be more likely to go with Terminal Services for a centralised solution.  For larger deployments I’d look at Citrix’s offering, even though you’re doubling those CAL costs.  But more often than not, a PC deployment is the way I’d still go.  You still need all the same management solutions and mechanisms no matter which way you go.  So I say go the way that’s cheapest, most trusted and more fault tolerant.

The basic problem is that server hardware is more expensive than PC hardware.  The only hope is that the power savings would write off the hardware purchase but I’ve no data for that.  I do know that PC’s are more efficient than ever.  We can control power usage using GPO and use WOL to power them up during the night to do updates.  And don’t forget there will always be a terminal on the desk (often an old, power inefficient recycled PC) for Terminal Services and VDI.

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