KVM-Guest runs extremly slowly


Hello everyone,

I am running KVM on a Debian Squeeze Host with 4 CPU-Cores and 8 GB RAM, RAID-1. The guest is a Windows 2003 Server machine, which was on bare metal before I virtualized it.

To transfer the machine, I did a dd if=/dev/hda on the old box, and then included the resulting 80-GB-File into the virtual machine one the new box.

The first weeks the system was running perfectly fast and responsive. Now, without having changed anything (I can prove this, I can show the logs :wink: ), the performance of the guest went more and more down, and now the guest takes at least one hour to start up, and it responds extremly slowly to mouse klicks.
The hard drives are noisy all the time while the guest is running, and it looks for me as if any RAM-Operation inside the guest would be done via swap on the disk, and not in the RAM itself. As soon I stop the guest, the disks are quiet.

Fact is that the host is not swapping:

top - 14:14:24 up 22:03, 1 user, load average: 0.24, 0.30, 0.33
Tasks: 117 total, 1 running, 116 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.7%us, 1.2%sy, 0.0%ni, 94.9%id, 3.0%wa, 0.0%hi, 0.1%si, 0.0%st
Mem: 8191364k total, 8107636k used, 83728k free, 22312k buffers
Swap: 1959912k total, 228k used, 1959684k free, 3730504k cached

The host is without problems responsive and fast, even while the guest is heavily accessing the disks.

Then, the Disk-Image-File is not so bad fragmented:

filefrag disk.img

disk.img: 37 extents found

The disk is included like this:

Has anyone any idea what is wrong here? What can be a reason for this behavior?

Thanks for any help!


Almost the same issue with Ubuntu 10.04 on Quad-core Phenom 12GB RAM. I am not sure, but I think that my Windows XP became slow after kernel update.