Hi Avi, I had missed to include some important syslog lines from the host system. See attachment.
On 03/10/10 14:15, Avi Kivity wrote: > > You have tons of iowait time, indicating an I/O bottleneck. > Is this disk IO or network IO? The rsync session puts a high load on both, but actually I do not see how a high load on disk or block IO could make the virtual hosts unresponsive, as shown by the hosts syslog? > What filesystem are you using for the host? Are you using qcow2 or raw > access? What's the qemu command line. > It is ext3 and qcow2. Currently I am testing with reiserfs on the host system. The system performance seems to be worse, compared with ext3. Here is the kvm command line (as generated by libvirt): /usr/bin/kvm -S -M pc-0.11 -enable-kvm -m 1024 -smp 1 -name test0.0 \ -uuid 74e71149-4baf-3af0-9c99-f4e50273296f \ -monitor unix:/var/lib/libvirt/qemu/test0.0.monitor,server,nowait \ -boot c -drive if=ide,media=cdrom,bus=1,unit=0 \ -drive file=/export/storage/test0.0.img,if=virtio,boot=on \ -net nic,macaddr=00:16:36:94:7e:f3,vlan=0,model=virtio,name=net0 \ -net tap,fd=60,vlan=0,name=hostnet0 -serial pty -parallel none \ -usb -vnc 127.0.0.1:0 -k en-us -vga cirrus -balloon virtio >>> >> How many virtual machines would you assume I could run on a >> host with 64 GByte RAM, 2 quad cores, a bonding NIC with >> 4*1Gbit/sec and a hardware RAID? Each vhost is supposed to >> get 4 GByte RAM and 1 CPU. >> > > 15 guests should fit comfortably, more with ksm running if the workloads > are similar, or if you use ballooning. > 15 vhosts would be nice. ksm is in the kernel, but not in my qemu-kvm (yet). > > Here the problem is likely the host filesystem and/or I/O scheduler. > > The optimal layout is placing guest disks in LVM volumes, and accessing > them with -drive file=...,cache=none. However, file-based access should > also work. > I will try LVM tomorrow, when the test with reiserfs is completed. Many thanx Harri