Performance of OS running from a booted VHD vs normal partition

Dragor1 · 13 Dec 2011

Hi folks!

Posting here after a long time!

As the title says, I am eager to know the performance (penalties or advantages) of running an OS booted from a VHD versus a normal partition installed OS.

Am thinking it would be a hassle free thing to try out Windows 8 once it enters beta, and since right now it would be a pain to allocate a new partition solely for Win 8 beta.

Also while I am at it, would also like to know if its possible to boot off a VHD residing in external flash media, and if yes, what are the restrictions for doing so (eg. Flash memory r/w params, min size, fs, etc.)

I tried a basic search but came up with way too much info. Will read through it after I get back home.

Thanks for your time, and cheers!

**cluberti** · 13 Dec 2011

As to the first question, there's a very small I/O performance penalty booting to a fixed-size VHD as there's an additional filter driver needed for the VHD usage as a hard disk rather than writing directly to a hard disk, but otherwise everything else will be the same as booting to a "native" OS disk. If you use a dynamic disk, there's a slightly more pronounced I/O penalty if the disk is growing during I/O operations.

As to the second question, if the device is capable of showing up as a fixed disk and is bootable it may work, although if it's not a fixed disk you will find adding it to the bcd is difficult (and booting to it, if anything changes, will invalidate the entry and fail to boot). Windows 8 provides this capability (Windows to Go) natively, but it really isn't easy to do (I have tried) with previous versions of Windows (VHD boot or otherwise).

Dragor1 · 22 Dec 2011

Thanks a lot, cluberti!

Will try a few things once win 8 reaches beta.

DeaconFrost · 23 Dec 2011

Why not just use a virtualization app? I despise multi-boot systems anymore, thanks to virtualization. That being said, if you have the .vhd, I believe the free VMWare Player will run it for you.

emaraszek · 23 Dec 2011

I've deployed several native boot dynamic VHD systems with no host OS. The one main thing I've noticed is that startup and shutdown take much longer than an identical system with a normal OS. (Optiplex 790, 4gb RAM, core i5, Windows 7 Enterprise) I've deployed these configs in pubic computing sites around our campus so that I can quickly update the image as needed, but I've never tried booting one off external media so I'm not sure how that would go

Another quirk with them is that you can't do a Windows experience index assessment which can be annoying if you want to enable Aero. The simple fix I found was to run "winsat.exe dwmformal" which will force the machine to check if it has Aero capabilities and then enable them if it does.

I'm just learning through technet articles and trial-and-error as I deploy these things so if I can be of any assistance let me know