I have VMWare Server 2 running on Ubuntu Jaunty desktop. The host is a core 2 quad with 2GB of RAM and two disks in RAID-0.

The guests are one Windows Server 2003 with 1 CPU, 700MB RAM and two SCSI disks of about 20GB each, and one Windows XP Pro with 1 CPU, 512MB RAM and one SCSI disk of about 20GB. There is not a great deal else happening on the box - it should be able to hold both memory images in physical RAM, I think, especially since it shows actual usage considerably less than what is allocated.

When I run either of these alone, everything goes very well; the guests are snappy and the web access page shows that the virtual CPU is running at around 1.6GHz - easily enough for my needs.

But when I try to run both of them simultaneously, the whole system grinds nearly to a halt. The two virtual CPUs between them manage about 250MHz (as shown by the web access page) either even split or about 200 to one and about 30 to the other. Needless to say, they are both unusably slow.

Digging around, the host's top shows that the CPUs are spending around 80-90% in iowait - with only one VM running this drops to about 3%. iotop shows that there are frequently up to about forty vmware-vmx threads all trying to read about 100KB/s, which probably explains things - the disks are madly dashing from place to place to fill all the requests. The overall transfer rate is pretty tame - about 2-4MB/s, well below the capabilities of the disks in sustained transfers.

Both virtual machines have:

sched.mem.pshare.enable = "FALSE"
mainMem.useNamedFile = "FALSE"

in their VMX files.

I've Googled for several hours and have found a number of people describing similar problems, but none with many solid suggestions and nothing that has made much difference (converting one VM from IDE to SCSI disks helped a little, but not significantly).

Can anyone suggest how to get these two to play nice together?