Today I run into a strange error where I was not able anymore to create new VMs with virt-manager: I always got an input/output error when I tried to start the machine after installation.
A look into /var/log/syslog showed quite some errors on the dm-device – note that my VMs disks usually are on logical volumes.
Sep 12 15:27:55 example kernel: [19298.163712] device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception. Sep 12 15:27:55 example kernel: [19298.243980] Buffer I/O error on device dm-5, logical block 1081985 Sep 12 15:27:55 example kernel: [19298.243983] lost page write due to I/O error on dm-5 Sep 12 15:27:55 example kernel: [19298.243994] Buffer I/O error on device dm-5, logical block 1081986 Sep 12 15:27:55 example kernel: [19298.243994] lost page write due to I/O error on dm-5
The fix is pretty easy: when you create the disk and thus the LV for the virtual machine, make sure you tell virt-manager that it should allocate the entire disk right from the start. It looks like sparse LV images are not supported right now.
/home/liquidat 