Howdy ! I have been trying for more than 2 days to work this out without success. While I am able to identify a qcow image as a block device within the guest, so far I can not use a qcow or qcow2 images as a block device due to IO errors. As a reference, I am able to mount raw images via loopback device through DOM0. Here is my setting: DOM0 - Xen 4.2.0 - Debian wheezy with 3.1.0-rc8 / 64bit [without blktap2 patch] - nfs mounted guest images DOM-U - PV - CentOS 6.2 with 2.6.33.20.x86_64 /, no initrd - no grub - Xen guest disk config: disk = [''format=raw,vdev=xvda,target=/dev/loop0'',''tap:qcow:/var/lib/xen-images/21339039-df03-43e2-b94f-2b600e2492b2/rootfs.qcow,xvdb,w'' When attempting to access the qcow backed device (xvdb) I get these errors: # less /var/log/messages ... Sep 19 01:26:15 kernel: [ 189.596610] Buffer I/O error on device xvdb, logical block 163967 Sep 19 01:26:15 kernel: [ 189.936239] end_request: I/O error, dev xvdb, sector 1311744 Sep 19 01:26:15 kernel: [ 189.940237] Buffer I/O error on device xvdb, logical block 163968 Sep 19 01:26:16 kernel: [ 190.276228] end_request: I/O error, dev xvdb, sector 1572864 ... Meanwhile, on DOM0 I see the following output in the process tree: ... root 911 2 0 01:49 ? 00:00:00 [blkback.59.xvda] root 848 1 0 01:49 ? 00:00:10 /usr/lib/xen/bin/qemu-system-i386 -xen-domid 59 -chardev socket,id=lib The block back-end kernel thread is backing my rootfs which is mapped to a loopback device on DOM0. I think qemu was launched to back the qcow device. Thus, this matches my conceptional understanding of how things should work. Ultimately, I am looking for a way to boot PVs from disk image using Xen 4.2. I was able to do this under Xen 4.1.x using a raw disk image in conjunction with the tap:aio option for the guests'' disk spec and without using a loopback mount on DOM0. Your help is much appreciated, Matthias _______________________________________________ Xen-users mailing list Xen-users@lists.xen.org http://lists.xen.org/xen-users