Short Tip: Fix input/output error while creating LVM backed VMs with libvirt

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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.

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2 thoughts on “Short Tip: Fix input/output error while creating LVM backed VMs with libvirt

  1. Thanks, I came across this error and unfortunately moved data into the unallocated space :/ Now I have to rescue the data somehow … But for the next time, I’ll know how to use libvirt correctly ;)

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