I've done some further tests and comparisons In this F19 based + ovirt stable repo the difference in qemu command line between the working run once with cd enabled of this CentOS 6.4 x86_64 and the normal run that doesn't proceed is: run once -drive file=/rhev/data-center/mnt/f18engine.mydomain:_var_lib_exports_iso/cc790a86-72e2-4aa2-a0b6-700756c399c3/images/11111111-1111-1111-1111-111111111111/CentOS-6.4-x86_64-bin-DVD1.iso,if=none,id=drive-ide0-1-0,readonly=on,format=raw,serial= -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0,bootindex=2 run -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw,serial= -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 A working normal run of a WinXP 32bit VM in another oVirt 3.2.3 environment is -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw,serial= -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 so it is the same as in 3.3. Possible problems: - 64bit OS I can try tomorrow to create a CentOS 6.4 32 bit and compare results - qemu default emulated pc version Some comparisons a) f18 host (AIO) with oVirt 3.2.3 qemu-kvm-1.2.2-14.fc18.x86_64 [root@tekkaman polimi]# qemu-kvm -machine ? Supported machines are: none empty machine pc Standard PC (alias of pc-1.2) pc-1.2 Standard PC (default) pc-1.1 Standard PC pc-1.0 Standard PC pc-0.15 Standard PC pc-0.14 Standard PC pc-0.13 Standard PC pc-0.12 Standard PC pc-0.11 Standard PC, qemu 0.11 pc-0.10 Standard PC, qemu 0.10 isapc ISA-only PC When I start WinXP (32bit of course) I see this command line: /usr/bin/qemu-kvm -name winxp -S -M pc-0.14 -cpu Opteron_G3 .... b) f19 host in oVirt 3.3 qemu-kvm-1.4.2-11.fc19.x86_64 [root@f18ovn03 ~]# qemu-kvm -machine ? Supported machines are: none empty machine pc Standard PC (i440FX + PIIX, 1996) (alias of pc-i440fx-1.4) pc-i440fx-1.4 Standard PC (i440FX + PIIX, 1996) (default) pc-1.3 Standard PC pc-1.2 Standard PC pc-1.1 Standard PC pc-1.0 Standard PC pc-0.15 Standard PC pc-0.14 Standard PC pc-0.13 Standard PC pc-0.12 Standard PC pc-0.11 Standard PC, qemu 0.11 pc-0.10 Standard PC, qemu 0.10 isapc ISA-only PC q35 Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-1.4) pc-q35-1.4 Standard PC (Q35 + ICH9, 2009) qemu command line for a CentOS 6.4 64bit vm is: /usr/bin/qemu-system-x86_64 -machine accel=kvm -name c6s -S -machine pc-1.0,accel=kvm,usb=off -cpu Opteron_G2 both /usr/bin/qemu-kvm and /usr/bin/qemu-system-x86_64 are in qemu-system-x86 rpm package. Questions: - given a version of oVirt, pc version in qemu generated command line is the same for every defined VM or is there any logic depending on OS chosen and/or bit (32 vs 64)? - if answer to previous question is fixed pc version, is there any particular reason to use pc-0.14 in oVirt 3.2.3 and pc-1.0 in oVirt 3.3 and not the latest available (so pc-1.2 in 3.2.3 and pc-1.3 or pc-i440fx-1.4 in 3.3)? - where can I find documentation about difference between the different pc-x.y versions? - can I use a wrapper in oVirt 3.3 to start VM with a different pc-x.y (eg pc-0.14) and see if anything changes helping debug and solve the problem? Thanks, Gianluca