Hi,
There certainly is some loss of performance to be expected.
Unfortunately there is not an easy answer on how much performance loss there would be as there are many factors.
To name just a few.
You have to take into account that the host OS (Windows 7) was not designed as a host for virtualisation.
Instead it was designed to be used as a desktop OS, so it is tuned for desktop use.
Then there can be a certain load at the host OS that will cause a slow down in the guest.
Eg. your physical hardware is bound to a certain number of Input/output operations per second, so if the host is reading/writing at the disk for another application then that means the maximum read/write performance that can be achieved will be less.
On top of that there's the extra layer. Your guest OS uses it's normal operating system calls to write to disk, but in reality it is just passing on those reads/writes to the host OS.
It is the host OS that does the writing.
Then there's the potential common performance measurements mistake.
For example if you take a few snapshots and then go try to do a read (or write) test, it will be much slower.
Why? Because now it has to read multiple times from disk in order to read that one sector from disk.
If you really want to get maximum performance then you probably should test with a pre-allocated disk as growing the virtual disk size while you are speed test writing to it will also slow things down.
On top of all that, your IO is now also more dependent on things like RAW CPU power, is your host or guest swapping to disk?
Is the RAM backing (.vmem) file being written too.
As you see, there's not an easy answer, but hopefully this gives you a bit of a better insight in things.
--
Wil
