KVM

Resize qcow2 with blockresize on running VM

Jeff — Wed, 09 Mar 2022 03:46:15 +0000

Resize qcow2 with blockresize on running VM Jeff Wed, 09/03/2022 - 05:46

So I sent an email to libvirt-users@redhat.com (there are some amazing wizards there!) and got an almost immediate response from Peter:

You can resize a QCOW2 (or any VM disk image) with virsh blockresize VM /path/to/image.qcow2 SIZE'.

This requires the VM to be running.

virsh blockresize ISPA /var/lib/libvirt/images/ispa.qcow2 300G

Result:
jeff@ispa-mx ~ $ sudo fdisk -l [sudo] password for jeff: Disk /dev/sda: 300 GiB, 322122547200 bytes, 629145600 sectors

Next, Install gdisk and cloud utils package for growpart, a Linux command line tool used to extend a partition in a partition table to fill available space.

apt install cloud-utils gdisk

Problem is that often/usually, in our case, the swap partition sits at the end of the disk, so it needs to be removed and added back after growing the primary data partition sda1.

root@ispa-mx:~# lsblk 
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0   300G  0 disk 
├─sda1   8:1    0 212.2G  0 part /
└─sda2   8:2    0   7.8G  0 part [SWAP]

Turn swap OFF.

swapoff -a

EDIT /etc/fstab and comment it OUT as a reboot may be required and it would hang the system because after recreating the partition the UUID will have changed!

Overview to end: Run fdisk, delete the swap, then recreate the swap partition at the end of the disk where it belongs. Write fdisk changes and run partprobe to get the kernel reinitialised with the change.

Then:

growpart /dev/sda 1 #Note the space

resize2fs /dev/sda1

Then fix the swap partition:

mkswap /dev/sda2 

Setting up swapspace version 1, size = 7.8 GiB (8389423104 bytes)
no label, UUID=5a00a73e-a01c-4900-8a63-ae76c42fa61f

Turn swap back on:

swapon -a

Note the new UUID. Edit /etc/fstab and update the swap UUID.

Fin.

Backup Virtual Machine

Jeff — Sun, 11 Nov 2018 08:21:51 +0000

Backup Virtual Machine Jeff Sun, 11/11/2018 - 10:21

Sources:

1. As root, locate the virtual machine you want to back up using virsh:

virsh -c qemu:///system list # shows only running

virsh list --all # shows all

2. Dump the configuration for your virtual machine:

virsh -c qemu:///system dumpxml MACHINE_NAME > /var/lib/libvirt/images/safe/MACHINE_NAME.datestamp.xml

3. You may need to locate the image directory:

virsh -c qemu:///system domblklist MACHINE_NAME

4. Now prepare the backup of this machine using a snapshot:

virsh snapshot-create-as --domain MACHINE_NAME IMAGE_NAME.snapshot --diskspec sda,file=/var/lib/libvirt/images/safe/IMAGE_NAME.snapshot.qcow2 --disk-only --atomic

Note: If you get an error, then the disk is not converted to virtio-scsi, and should be vda, not sda.

After creating the snapshot, all disk operations from the guest will be directed to it so that you can copy the original disk image to a safe place.

You can establish this by running, as example:

virsh -c qemu:///system domblklist ispa

Target     Source
------------------------------------------------
hda        -
sda        /var/lib/libvirt/images/safe/ispa.snapshot.qcow2

5. Copy to external server and include both the qcow2 disk image and the machine configuration (the XML file):

su - yourusername # you must be in libvirt-qemu group

rsync -hav --progress /var/lib/libvirt/images/IMAGE_NAME.qcow2 192.168.100.2:backups/ # IP address of prionyx on 1GB VLAN

6. Merge snapshot:

After the file transfer is completed, you should merge changes written to snapshot, back to original disk image. This operation is called 'active block commit':

virsh blockcommit MACHINE_NAME sda --active --pivot --shallow --verbose

Check block devices again. If the block commit completed successfuly your virtual machine should use its original image again.

virsh -c qemu:///system domblklist MACHINE_NAME

Example Backup script for running VMs:

jeff@sheri:~$ cat /var/lib/libvirt/images/scripts/ispa.backup.sh 
#!/bin/bash
################################################################################
#
# This script takes a snaphot of the running VM, which leaves the main qcow2
# image in a known state. All VM activity is then recorded in the snapshot,
# while the main qcow2 image can be rsync'd to a remote backup server.
# After the image has been transferred, the snapshot is merged back to the
# main image, and then deleted.
#
# NB. This script must be run by a user who is a member of libvirt-qemu group.
#
################################################################################


virsh -c qemu:///system dumpxml ISPA > /var/lib/libvirt/images/xml/ispa.xml
scp /var/lib/libvirt/images/xml/ispa.xml 192.168.100.4:/var/lib/libvirt/images/xml/
virsh snapshot-create-as --domain ISPA ISPA.snapshot --diskspec sda,file=/var/lib/libvirt/images/snapshots/ispa.snapshot.qcow2 --disk-only --atomic
rsync --rsync-path="ionice -c 3 nice rsync" -havW --progress /var/lib/libvirt/images/ispa.qcow2 192.168.100.4:/var/lib/libvirt/images/sheriff/
virsh blockcommit ISPA sda --active --pivot --shallow --verbose
virsh snapshot-delete ISPA --metadata ISPA.snapshot
rm -rf /var/lib/libvirt/images/snapshots/ispa.snapshot.qcow2
#rm /var/lib/libvirt/images/xml/ispa.xml

KVM Bridged Networking

Jeff — Mon, 18 Jun 2018 12:14:07 +0000

KVM Bridged Networking Jeff Mon, 18/06/2018 - 14:14