How important is Directed I/O (VT-d) for desktop VMs?

[Sta5h]

Hi,

I'm contemplating replacing my desktop with a laptop and the new Dell XPS 15 (xps-L502x) range with SNB cpus seems to tick most of the boxes (I'll replace the HDD with an SSD and up the RAM to 8GB myself thanks).

However, as I use VMWare workstation to test out various linux builds (desktops and NASs) along with a few different versions of windows/IE for web development, I'm wndering how much of a difference the "Intel® Virtualization Technology for Directed I/O (VT-d)" will make to me.

The Core i7 2630QM doesn't have this tech, but the Core i7 2720QM does - however it's an extra £160. Is this going to be worth it for me?

The additional MHz speed of the 2720 over the 2630 is worth zero to me, so it's really all about how much of a difference the extra virtualisation tech is going to make.

I'd appreciate some responses from people who have actually seen the difference of running both with and without this as I'd really like t save myself £160 if I can

Thanks in advance.

 

[drizek]

http://en.community.dell.com/support-forums/laptop/f/3518/p/19346144/19749210.aspx

You should make sure the Laptop hardware supports it before spending extra on the CPU.

 

[IntelEnthusiast]

VT-d is all about helping to stop conflict with VMs trying to access the same hardware at the same time (DMAs). So easy answer is that unless you are running a number of VMs (let’s say something like 4 or 5) you shouldn't run into a problem with VT-d and in a laptop. In the desktop and laptop space for the vast majority of people VT-d only real value is that it is part of the requirements for a computer based on the Intel vPro technology for use in a business environment. To run a VM the only thing that is required is VT-x the basic support for virturalization.

Christian Wood
Intel Enthusiast Team

 

[Sta5h]

Thank you both for your answers.

Thanks IntelEnthusiast: I think that pretty much settles it, I'll save myself £160 and put it towards the SSD instead I can't see myself running more than 3-4 VMs at one time ever (especially on 8GB RAM) and if they are, they're not going to be doing anything particularly heavy anyway.

I hadn't even thought it a possibility that the laptop *wouldn't* support the feature, so thanks for that left-field heads-up drizek.

 

[Voo]

For testing out different OSes or setting up a sandboxed webbrowser? Absolutely uninteresting. Sure you may lose a few percentage on IO heavy uses with several VMs, but for your usage scenario you hardly care about that.

Also depending on your used software (eg VMWare) and if you're fine without 64bit guest OSes you can do without VT-x. Although I think Intel finally stopped their madness and at least included that basic feature everywhere - one example of extremely annoying market segmentation that was..

 

[Sta5h]

I will be using 64bit guests but that's a non issue as you mention that everything seems to have VT-x now. Thanks for the info