Hi all. Presently, 7 VMs (4 windows, 3 ubuntu) are using the same nfs pool. The machine serving that NFS pool (VLET1) has high load as soon as there is some continuous disk activity: top - 13:25:30 up 23:16, 5 users, load average: 4.51, 4.41, 3.98 Tasks: 191 total, 1 running, 189 sleeping, 0 stopped, 1 zombie Cpu0 : 3.0%us, 2.6%sy, 0.0%ni, 44.6%id, 49.8%wa, 0.0%hi, 0.0%si, 0.0%st Cpu1 : 4.2%us, 2.9%sy, 0.0%ni, 54.2%id, 38.1%wa, 0.0%hi, 0.6%si, 0.0%st Cpu2 : 3.6%us, 2.3%sy, 0.0%ni, 55.4%id, 38.7%wa, 0.0%hi, 0.0%si, 0.0%st Cpu3 : 2.9%us, 4.2%sy, 0.0%ni, 56.4%id, 36.5%wa, 0.0%hi, 0.0%si, 0.0%st It's a quad-core Xeon, running SW Raid on sataII disks: cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sdb1[1] sda1[0] 966796224 blocks [2/2] [UU] When the VM client's disk activity is low, the load on VLET1 is very minimal: top - 13:53:30 up 23:44, 5 users, load average: 0.11, 0.81, 1.83 Tasks: 191 total, 1 running, 189 sleeping, 0 stopped, 1 zombie Cpu0 : 1.0%us, 2.0%sy, 0.0%ni, 92.1%id, 4.6%wa, 0.0%hi, 0.3%si, 0.0%st Cpu1 : 2.2%us, 5.3%sy, 0.0%ni, 90.7%id, 1.9%wa, 0.0%hi, 0.0%si, 0.0%st Cpu2 : 4.2%us, 3.6%sy, 0.0%ni, 87.7%id, 4.5%wa, 0.0%hi, 0.0%si, 0.0%st Cpu3 : 3.2%us, 3.2%sy, 0.0%ni, 93.3%id, 0.3%wa, 0.0%hi, 0.0%si, 0.0%st What can I do to reduce the load? Now, sometimes a VM refuses to come up (windows blue screen) except when I launch it on the same host (VLET1) hosting the nfs share. After booting the VM, I can live migrate it to another VM host, eg VLET2. I did spot an error in /var/log/messages at boot failure of the windows VM when starting it on VLET2: Mar 10 11:06:46 VLET2 libvirtd: 11:06:46.137: warning : qemudParsePCIDeviceStrs:1422 : Unexpected exit status '1', qemu probably failedbut I'm not sure this is related. This is a test config; our company's mail server will soon be running in this cluster of KVM hosts (VLET1 and VLET2 will be joined by VLET3 next week). Since the Domino mail server is very disk intensive, I'm a bit worried now. I would rather not run it on local disks, sionce this makes live migration impossible. I'll need to decide where to put the storage pool, and using which protocol (NFS or iSCSI). Which brings me to my last question: I was wondering whether it would be better to use iSCSI instead of NFS? I started with this, but couldn't get a pool defined through virt-manager (it always showed as 100% full, even when I created a completely new iSCSI target/lun). According to e.g. <a href=http://communities.vmware.com/thread/150775>http://communities.vmware.com/thread/150775</a> it doesn't seem to make much difference, whether I use iSCSI or NFS, performance-wise. Anyhow, I don't grasp how KVM running on different hosts, connected to the same iSCSI LUN, can work? It corrupts data, having the same LUN mounted on different hosts... I obviously understood something wrong about iSCSI... Regards, Jürgen