[libvirt-users] add disk problems for domain

hi,all I use Java api `domain.attachDeviceFlags(xml, 0);` to add a disk for domain. the xml file like this: <disk type='file' device='disk'> <driver name='qemu' type='raw'/> <source file='/dev/sp1353486595267/v1353488096262'/> <target dev='vdb' bus='virtio'/> </disk> then I use command `virsh detach-disk $domain vdb` to remove the disk. what I said above have no any errors.but the problem is when I restart this vm ,the disk still exist,because I see it from the command `virsh dumpxml $domain` ,how to remove the disk from this domain persistently. thanks in advance.