Answer to myself. Troubleshooted the symptom with my colleague and found the root cause. In case of libvirt update from 0.6.3 to 0.8.2, I had to restart my Guest OS. Otherwise I got an error when I execute attached-disk with libvirt 0.8.2. > error: Failed to attach disk > error: internal error missing disk device alias name for hdc It was because virDomainDeviceInfo info in struct _virDomainDiskDef was NOT exist in 0.6.3. After update, libvirt 0.8.2 does origdisk->info.alias, and it causes this error message. I believe there are many changes between 2 versions. So I conclude that it is safe to stop Guest OS when libvirtd is updated. Thanks Masanari
