[libvirt-users] memory snapshot save error

libvirt version: 3.4.0 architecture: x86_64 ubuntu16.04-server hypervisor: kvm,qemu when I want make a memery snapshot for a vm ,and I call virsh save ,but tell me this error: error: Failed to save domain 177 to /datapool/mm.img error: operation failed: domain save job: unexpectedly failed xml configure: <domain type='kvm' id='177'> <name>virt23</name> <uuid>e50c1d59-c4a3-4413-b6c9-20e90cced343</uuid> <metadata/> <memory unit='KiB'>10485760</memory> <currentMemory unit='KiB'>10485760</currentMemory> <vcpu placement='static'>1</vcpu> <resource> <partition>/machine</partition> </resource> <os> <type arch='x86_64' machine='pc-i440fx-2.5'>hvm</type> <boot dev='hd'/> </os> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>destroy</on_crash> <devices> <emulator>/usr/bin/kvm</emulator> <disk type='file' device='disk'> <driver name='qemu' type='raw'/> <source file='/datapool/zhuohf/virt23.qcow2'/> <backingStore/> <target dev='vdc' bus='virtio'/> <alias name='virtio-disk2'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> <disk type='file' device='cdrom'> <driver name='qemu' type='raw'/> <source file='/datapool/zhuohf/ubuntu-16.04.2-desktop-amd64.iso'/> [40/38156] <backingStore/> <target dev='hdc' bus='ide'/> <readonly/> <alias name='ide0-1-0'/> <address type='drive' controller='0' bus='1' target='0' unit='0'/> </disk> <controller type='usb' index='0' model='piix3-uhci'> <alias name='usb'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 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> <interface type='network'> <mac address='52:54:00:e0:31:68'/> <source network='default' bridge='virbr0'/> <target dev='vnet11'/> <model type='rtl8139'/> <alias name='net0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/> </interface> <input type='mouse' bus='ps2'> <alias name='input0'/> </input> <input type='keyboard' bus='ps2'> <alias name='input1'/> </input> <graphics type='vnc' port='5909' autoport='yes' listen='0.0.0.0'> <listen type='address' address='0.0.0.0'/> </graphics> <video> <model type='cirrus' vram='16384' heads='1' primary='yes'/> <alias name='video0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/> </video> <memballoon model='virtio'> <stats period='1'/> <alias name='balloon0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/> </memballoon> </devices> <seclabel type='none' model='none'/> <seclabel type='dynamic' model='dac' relabel='yes'> <label>+0:+0</label> <imagelabel>+0:+0</imagelabel> </seclabel> </domain> before I encounter the same error,that time is my disk not free space，but this time I can't find error reason. Thanks