I have 2 types of hosts as below ( each is 64 bits processor . number of processor is not equal . First has 1G memory . the second 3 G memor): IBM blade HS21 with Intel Xeon L5320 (1,86Ghz) . 8 processors (blade) IBM desktop with Intel(R) Core(TM)2 Duo CPU E6550 @ 2.33GHz I have generated an Ubuntu 8.10 client image on the first . It runs smooth on the first via virsh . It runs ok on the second but not well via virsh ( define + start <xml> ). just by a direct : sudo qemu-system-x86_64 call . If I generate a similar image on the second host (using same .iso Ubuntu CD image) then it runs on the first and second host smoothly via virsh (define + start <xml>) Is there an explanation for that ? Also : please comment if the below qemu-system-x86_64 explicit image start of a VM and the same done by a virsh command by : define + start <.xml> are equivalent and if not what change should I make to the .xml file (below) 1. sudo qemu-system-x86_64 -hda <path/to/image/file> -m 512 -net nic, model=e1000 -nic tap 2. The xml file thanks Zvi Dubitzky Virtualization and System Architecture Email:dubi@il.ibm.com IBM Haifa Research Laboratory Phone: +972-4-8296182 Haifa, 31905, ISRAEL