Sysadmin/Migrate virtual machine: Difference between revisions
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=== Importing an existing disk image into libvirt === | |||
Let's assume you already have a disk file and you want to add it to a pool. | |||
There doesn't seem to be a direct way to do this with virsh, but you can create a blank disk and then copy your image into it: | |||
# virsh vol-create-as boot new.img 1G --format raw | |||
# virsh vol-upload --pool boot new.img existing.img | |||
=== Copying LVM volumes across machines === | |||
Create the new volume, format and mount it: | |||
# virsh vol-create-as nvme-pool new-root 20G | |||
# mkfs.ext4 -L new-root -O mmp,flex_bg,extent,uninit_bg,sparse_super /dev/nvme-pool/new-root | |||
# tune2fs -c -1 -i 0 /dev/nvme-pool/new-root | |||
# mkdir /new-root | |||
# mount /dev/nvme-pool/new-root /new-root | |||
Copy the contents of the remote filesystem (this can be done while the VM is online, but you might want to shutdown any running database to get a consistent snapshot): | |||
# rsync -PHAXphax lightwave:/ /new-root/ | |||
Don't forget to unmount your new filesystem! | |||
# umount /new-root | |||
# rmdir /new-root | |||
=== Importing a VM from existing disk files === | |||
# virt-install -v --accelerate --nographics --vcpus 2 --ram 1024 --os-type linux --os-variant=ubuntu20.04 --network bridge:br0 --disk vol=boot/NEWVM-boot.img,bus=virtio --disk vol=nvme-pool/NEWVM-root,bus=virtio --name NEWVM --import | |||
The new VM will boot and probably fail to mount the root because the UUID changed. | |||
You can fix this by dropping into grub the usual way: | |||
* virsh start --console NEWVM | |||
* press ESC before the kernel starts | |||
* press e to edit a menu entry | |||
* modify the kernel command line (for example, root=/dev/vdb) | |||
* hit ctrl-x to boot | |||
After booting, remember to update your grub.cfg and test it: | |||
# update-grub | |||
# reboot | |||
=== How to migrate a file-based guest to LVM (online method) === | === How to migrate a file-based guest to LVM (online method) === | ||
* First, | * First, take a copy of the kernel and initrd: | ||
treehouse# scp VMNAME:/boot/{vmlinuz,initrd}-2.6.31-22-server /srv/vm/kernel/ubuntu/ | treehouse# scp VMNAME:/boot/{vmlinuz,initrd}-2.6.31-22-server /srv/vm/kernel/ubuntu/ | ||
* Then, create the logical volume and attach it to the running VM: | |||
treehouse# virsh vol-create-as treehouse VMNAME-root 10G | treehouse# virsh vol-create-as treehouse VMNAME-root 10G | ||
treehouse# virsh attach-disk VMNAME /dev/treehouse/VMNAME-root vdc | treehouse# virsh attach-disk VMNAME /dev/treehouse/VMNAME-root vdc | ||
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=== How to migrate a file-based guest to LVM (offline method) === | === How to migrate a file-based guest to LVM (offline method) === | ||
This method works by taking down the virtual machine during the migration and mounting the | |||
partition inside the hard drive image. Mounting qcow2 files require a fancier method. | |||
* Determine the offset of the root partition within the raw disk image: | * Determine the offset of the root partition within the raw disk image: | ||
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mount -o loop,offset=$((63 * 512)) vm.img /mnt/ | mount -o loop,offset=$((63 * 512)) vm.img /mnt/ | ||
* Then create an LV and copy over everything as in the online case | * Then, create an LV and copy over everything as in the online case | ||
virsh vol-create-as treehouse VMNAME-root 10G | |||
virsh attach-disk rt /dev/treehouse/VMNAME-root vdc | |||
mkfs.ext4 -L rt-root -O flex_bg,extent,uninit_bg,sparse_super /dev/treehouse/VMNAME-root | |||
tune2fs -c -1 -i 0 /dev/treehouse/VMNAME-root | |||
mkdir /mnt2/VMNAME-root | |||
mount /dev/treehouse/VMNAME-root /mnt2/VMNAME-root/ | |||
rsync -HAXphax --numeric-ids --delete /mnt/VMNAME-root/ /mnt2/VMNAME-root/ | |||
=== How to migrate an LVM-based guest to another host === | === How to migrate an LVM-based guest to another host === | ||
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=== Alternative to convert file based VM to block based LVM | === Alternative to convert file based VM to block based LVM === | ||
Stop the VM | Stop the VM | ||