Sizing memory for virtual machines appropriately

re: Sizing memory for virtual machines appropriately

VPC User — Fri, 23 Sep 2005 05:42:06 GMT

Excellent post!

The only question is what are the optimal sizes for all of the main OSes Virtual PC had in the Wizard menu? Is 128 MB good enough for XP and 64 MB for Windows 98?

re: Sizing memory for virtual machines appropriately

Norman DIamond — Fri, 23 Sep 2005 07:17:50 GMT

> Virtual PC and Virtual Server wire down the
> memory that they use for each virtual machine

That is true. And therefore:

> If a guest operating system needs to page
> excessively then it is going to cause that
> virtual machine to run slowly.

Actually it will also cause the the real machine to run slowly, because the real machine's excessive paging will be competing with the guest machine's excessive paging and everyone will lose.

VPC User asked:
> Is 128 MB good enough for XP and 64 MB for
> Windows 98?

That depends on what you want to do in them. To run VS2005 (where VS = Visual Studio) betas, I needed a minimum of 256 MB for a release build of XP in a guest machine, or 384 MB for a checked build. To run a few simple executables that I built and just verify whether they run in Windows 98, 64 MB was enough for those guests (and probably 32 MB would be enough).

re: Sizing memory for virtual machines appropriately

Ray — Fri, 23 Sep 2005 08:39:25 GMT

To fully understand your explanation: "Repeat the above process inside of each of the virtual machines that you intend to run."

I have a virtual machine currently allocated 523MB and available 324MB. (all needed applications running)

Will this mean +/- 300MB of memory would be enough?
(523-324+100=299)

And what about the page file on the virtual machine? Is there also a golden rule...
Ray

re: Sizing memory for virtual machines appropriately

Virtual PC Guy — Fri, 23 Sep 2005 08:52:22 GMT

Norman -

Your point about guest paging is only true if the host is paging as well. If you have enough memory for the host - but not enough memory for the guest then only the guest will page and the host will be fine.

Ray -

Yup - that is what I mean. As for the page file in the virtual machine my advice is always to let Windows manage the page file. It knows what is best to do.

Cheers,
Ben

re: Sizing memory for virtual machines appropriately

Simon — Fri, 23 Sep 2005 09:14:27 GMT

Would also be nice to hear about CPU sizing. Its usually quite hard to know how much processing power you need on a host when you consolidate phisical servers into virtual ones.
Any tips and trick on this matter?

Simon

re: Sizing memory for virtual machines appropriately

Christopher Lewis — Fri, 23 Sep 2005 20:12:49 GMT

You've stated that VPC pins the memory so it's not swapped.

I'm often doing development, and have a VPC instance running in the background. While I'm not using it, I pause the VPC. I know this opens up a lot of CPU cycles, but is the memory un-pinned while it's paused?

I'm on a 1.5 GB box, but w/ VPC running and VS 2003, there's not a lot of room :-)

Also, why can't you see where VPC's memory is in the task mananger? If I've got a 384mb Virtual machine running, why doesn't the VPC process show that memory?

re: Sizing memory for virtual machines appropriately

Candle — Sat, 24 Sep 2005 17:27:30 GMT

> Excessive paging == bad

> In fact it is very good. What is bad is when you configure a system with so little memory that it is forced to page excessively. This will result in the entire performance of your system being bottle necked around the speed of your hard disk (which is about the slowest thing in your system).

If you're trying to keep your virtual machine images / snapshots / deltas as small as possibly any paging can be bad as it can increase the size of your saved virtual machines just because you happened to be using a lot of memory at a certain moment in time.

re: Sizing memory for virtual machines appropriately

Candle — Sat, 24 Sep 2005 17:27:46 GMT