Realy slow writes on cache SSD in Windows VM

I'm getting really terrible write speeds inside my windows VM. The read speeds are great 1.8GB/s, but the writes don't get above 50kb/s. If I run the following command on unraid I get a more reasonable write speed.

Quote

dd if=/dev/zero of=/mnt/cache/test.dd count=8192000 bs=64k count=8k
8192+0 records in
8192+0 records out
536870912 bytes (537 MB, 512 MiB) copied, 0.266534 s, 2.0 GB/s

Quote

root@R720:~# dd if=/dev/zero of=/mnt/cache/test.dd count=8192000 bs=64k count=80k
81920+0 records in
81920+0 records out
5368709120 bytes (5.4 GB, 5.0 GiB) copied, 5.09313 s, 1.1 GB/s

 

But In the windows VM, when I run CrystalDiskMark it will even timeout the RDP session, and freeze the VNC session, until the test is done. All the read speeds are 500MB/s or higher but all the write speeds are either 0MB/s or 1MB/s.

This is my config:

<?xml version='1.0' encoding='UTF-8'?>
<domain type='kvm' id='1'>
  <name>Windows 10</name>
  <uuid>91b82e52-7a3d-d320-f943-ff2320c3395b</uuid>
  <metadata>
    <vmtemplate xmlns="unraid" name="Windows 10" icon="windows.png" os="windows10"/>
  </metadata>
  <memory unit='KiB'>33030144</memory>
  <currentMemory unit='KiB'>33030144</currentMemory>
  <memoryBacking>
    <nosharepages/>
  </memoryBacking>
  <vcpu placement='static'>12</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='6'/>
    <vcpupin vcpu='1' cpuset='18'/>
    <vcpupin vcpu='2' cpuset='7'/>
    <vcpupin vcpu='3' cpuset='19'/>
    <vcpupin vcpu='4' cpuset='8'/>
    <vcpupin vcpu='5' cpuset='20'/>
    <vcpupin vcpu='6' cpuset='9'/>
    <vcpupin vcpu='7' cpuset='21'/>
    <vcpupin vcpu='8' cpuset='10'/>
    <vcpupin vcpu='9' cpuset='22'/>
    <vcpupin vcpu='10' cpuset='11'/>
    <vcpupin vcpu='11' cpuset='23'/>
  </cputune>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-i440fx-3.0'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi.fd</loader>
    <nvram>/etc/libvirt/qemu/nvram/91b82e52-7a3d-d320-f943-ff2320c3395b_VARS-pure-efi.fd</nvram>
  </os>
  <features>
    <acpi/>
    <apic/>
    <hyperv>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
      <vendor_id state='on' value='none'/>
    </hyperv>
  </features>
  <cpu mode='host-passthrough' check='none'>
    <topology sockets='1' cores='6' threads='2'/>
  </cpu>
  <clock offset='localtime'>
    <timer name='hypervclock' present='yes'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/local/sbin/qemu</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source file='/mnt/user/domains/Windows 10/vdisk1.img'/>
      <backingStore/>
      <target dev='hdc' bus='virtio'/>
      <boot order='1'/>
      <alias name='virtio-disk2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/isos/Windows 10.iso'/>
      <backingStore/>
      <target dev='hda' bus='ide'/>
      <readonly/>
      <boot order='2'/>
      <alias name='ide0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/isos/virtio-win-0.1.141.iso'/>
      <backingStore/>
      <target dev='hdb' bus='ide'/>
      <readonly/>
      <alias name='ide0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <alias name='usb'/>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <alias name='usb'/>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <alias name='usb'/>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'>
      <alias name='pci.0'/>
    </controller>
    <controller type='ide' index='0'>
      <alias name='ide'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='sata' index='0'>
      <alias name='sata0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <alias name='virtio-serial0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:8d:1c:c4'/>
      <source bridge='br0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/0'/>
      <target type='isa-serial' port='0'>
        <model name='isa-serial'/>
      </target>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/0'>
      <source path='/dev/pts/0'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-1-Windows 10/org.qemu.guest_agent.0'/>
      <target type='virtio' name='org.qemu.guest_agent.0' state='disconnected'/>
      <alias name='channel0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
      <address type='usb' bus='0' port='1'/>
    </input>
    <input type='mouse' bus='ps2'>
      <alias name='input1'/>
    </input>
    <input type='keyboard' bus='ps2'>
      <alias name='input2'/>
    </input>
    <graphics type='vnc' port='5900' autoport='yes' websocket='5700' listen='0.0.0.0' keymap='en-us'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
    </memballoon>
  </devices>
  <seclabel type='dynamic' model='dac' relabel='yes'>
    <label>+0:+100</label>
    <imagelabel>+0:+100</imagelabel>
  </seclabel>
</domain>

Does anyone have an idea, why my writes speeds inside the VM are so terrible? 

Edited October 8, 20187 yr by Jurre