Hi, Thanks so much for your detailed explanation! Best regards, Richard Taubo > On 30 Nov 2019, at 10:25, Peter Krempa <pkrempa@xxxxxxxxxx> wrote: > > On Sat, Nov 30, 2019 at 01:12:31 +0100, ort_libvirt@xxxxxxxxxxxx wrote: >> Hi! >> >> I need to convert a KVM virtual machine from LVM to a qcow2 image, and wonder if this is the best way to do it (*1): >> [$] qemu-img convert -O qcow2 /dev/vg_name/lv_name/ /var/lib/libvirt/images/image_name.qcow2 >> >> If this is the best way to do this, will this keep the information on: /dev/vg_name/lv_name/ untouched? > > As long as you also reconfigure the VM to use > /var/lib/libvirt/images/image_name.qcow2 after this point the old > logical volume will not be used. > > The above approach is good if you are okay with some downtime on the VM > while the image is converted over. > > There are a few other approaches you can conisder when you want to do it > live or for example save some space in the qcow2 image by using fstrim > first. > > For a live conversion, you can do an external disk-only snapshot first > which creates a qcow2 overlay file: > > virsh snapshot-create-as $VMNAME --no-metadata --disk-only --diskspec > $DISK,file=/path/to/image.qcow2 --diskspec ... > > Optionally if your disk frontend supports it [1] and you've configured it > properly you can now run 'fstrim' on the filesystems. That records which > parts of the disk are empty into the overlay file and thus will not be > converted later > > After that you pull the backing image into the qcow2: > > virsh blockpull --wait --verbose $DOMNAME $DISK > > if you executed the trim step the image will be smaller and also the > conversion step will avoid copying unused parts. Optionally that step > can be skipped and then the result will be the same as in the offline > conversion approach. > > Optionally if you don't care about the trim step above you can use also > the 'blockcopy' operation instead of the two steps above to achieve the > same: > > virsh blockcopy $VMNAME $DISK --dest /path/to/new.qcow2 --wait --verbose > --pivot --format qcow2 --transient-job > > Also if you want to decrease the size after an offline coversion you can > use the 'virt-sparsify' tool from the libguestfs suite on the image if > the VM is offline. > > [1] You must have at least qemu-4.0 if you want to use fstrim on a > virtio-blk disk interface, or switch to virtio-scsi based disks. Also > your disks must have the 'discard="unmap"' option in the <driver> > element of your vm's XML. > > I've used the above approach to convert few production VMs from LVs to > qcow2 for moving them to a different host later on. Apart from a sub 1 > minute downtime to restart the VM to switch to virtio-scsi from > virtio-blk to enable support for trimming the images the conversion was > then executed while the VM were running. Obviously if you don't require > this you can easily go with the qemu-img approach. _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
