Speeding up VPC with multiple hard drives?

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anon050413@mac.com - 13 Apr 2005 16:02 GMT

A long time ago, one of the speed tips on Windows systems was to
install multiple hard drives. Putting the virtual memory swap file on
one hard drive and the rest of the operating system on another could
make a big difference.

Would the same trick work with Virtual PC 7 on the Mac? Say I have two
PHYSICAL hard drives on my system. I create a Virtual Machine with two
VIRTUAL hard drives, and store each of those on the separate physical
disks.

Can I get a speed improvement this way?

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William Smith - 14 Apr 2005 02:42 GMT

> A long time ago, one of the speed tips on Windows systems was to
> install multiple hard drives. Putting the virtual memory swap file on
[quoted text clipped - 7 lines]
>
> Can I get a speed improvement this way?

If the hard drive were the bottleneck then yes, this would speed up VPC,
but it's the emulation of the Intel processor that makes VPC slow.

You may get a slight performance increase but I wouldn't bank on a
dramatic improvement.

bill

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William M. Smith
(Microsoft Interop MVP)

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Richard Cardona - 14 Apr 2005 03:41 GMT

It depends on the demands of your applications. The biggest performance
bottleneck, IMO is CPU emulation not disk or net i/o. Unless you doing a
lot of disk i/o speeding up the disk is not a worthy investment.

One thing I've read (but don't have the RAM to spare) is to put the VPC app
in a RAM disk. The means the normally memory-mapped application is fully
loaded in RAM and runs at RAM speeds instead of paging in as needed.

If you combine this putting XP's swap on the same RAM disk, it might be
quite fast but at quite a host RAM hog expense.

Richard

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anon041405@mac.com - 14 Apr 2005 17:36 GMT

Richard Cardone wrotye (in part)

> The biggest performance bottleneck, IMO is CPU emulation
> not disk or net i/o. Unless you doing a lot of disk i/o speeding
> up the disk is not a worthy investment.

Yes and no. Yes, CPU emulation is a huge bottleneck and optimizing
disk I/O won't help that.

BUT Windows 98/NT/2000/XP atc... all do a huge amount of disk I/O for
page swaps, regardless of what you THINK your applications are doing..
In VPC, if you allocate a lot of memory to your virtual machine, the
swap file is likewise huge.

Try this on your own: Add a second virtual drive to your virtual
machine. Make it FAT32, FIXED size of either 512M or 1G. Then in
Windows, set the swap file size on your C drive to nothing (or a max of
2M), and the swap file size on your D drive to 1.5 times the amount
memory allocated to your virtual machine. Reboot the virtual machine.

This is a reasonable optimization even with ONE physical hard drive, it
makes Windows notieably more responsive. I haven't tried it with two
physical drives, but I believe if you did it would be a MUCH more
noticeable speedup.

Anyone else tried this?

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Tony Kavadias - 27 Apr 2005 11:17 GMT

> One thing I've read (but don't have the RAM to spare) is to put the VPC app
> in a RAM disk. The means the normally memory-mapped application is fully
> loaded in RAM and runs at RAM speeds instead of paging in as needed.

So, on Mac OS X, how is this possible?!

;-)

BTW, Virtual PC already locks down RAM once it's loaded... the locked-down
RAM represents the physical memory space of a PC. This is done to prevent
"double-faulting" from slowing your virtual PC down.

In this case, a "double-fault" is a page fault within the virtual PC
which causes a
real page fault to occur in the Mac itself.

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-- tonza.

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Mac Forum / Applications / Virtual PC / April 2005

Speeding up VPC with multiple hard drives?