CentOS 8.x KVM Creating Windows VMs with fast disk input output (io)

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CentOS 8.x KVM Creating Windows VMs with fast disk input output (io)

While creating Windows VM use following recommendations along with mentioned references

• Use virtio drivers for Windows KVM VMs

  https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win.iso

• Make sure metadata space is pre-allocated in case of qcow2 disk images

  https://serverfault.com/questions/407842/incredibly-low-kvm-disk-performance-qcow2-disk-files-virtio

• Make sure cache is set to none (Preferred). Cache option of write-through has very bad performance. Using write-back may lead to data loss in case of abrupt shutdown.

  http://www.ilsistemista.net/index.php/virtualization/11-kvm-io-slowness-on-rhel-6.html?start=4

  https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.ldvq/ldvq_kvm_quick_start.html

• IO Mode to native

  https://georgik.rocks/solution-kvm-guest-io-very-slow/

  https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.ldvq/ldvq_kvm_quick_start.html

• Avoid use of IOthreads as explained at

  https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.ldvq/ldvq_kvm_quick_start.html

  https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.ldva/ldva_t_definingGuestDevices.html

  This gives error that iothreads are not supported in latest CentOS 7

• Setting CPU model to host-model (host-passthrough) or core2duo might improve things CentOS 7.x Cloudstack 4.11 Guest VM CPU configuration for Windows

  https://forums.unraid.net/topic/36777-kvm-windows-guests-100-disk-in-task-manager-and-very-slow/

• There are some hyper-V related settings suggested at

  https://forums.unraid.net/topic/36777-kvm-windows-guests-100-disk-in-task-manager-and-very-slow/

  They seem to come by default if you select Guest OS as Windows 10 during VM creation

• Specifically for Windows 10 all of above also leads to marginal performance. Changing disk from qcow2 to raw has dramatic speed improvements (upto 10x). If snapshots are must then use LVM instead of raw format.

  https://serverfault.com/questions/425607/kvm-guest-io-is-much-slower-than-host-io-is-that-normal

  https://serverfault.com/questions/407842/incredibly-low-kvm-disk-performance-qcow2-disk-files-virtio

  https://pve.proxmox.com/wiki/Performance_Tweaks

  https://unix.stackexchange.com/questions/47082/how-to-improve-windows-perfomance-when-running-inside-kvm

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