Increase the size of a VM's disk
Note: Both methods have the risk to break the whole VM so it's best to make a backup first.
Method 1
First of all take a note of the VM's partition that you want to increase. On guest run:
# df -h Filesystem Size Used Avail Use% Mounted on udev 479M 0 479M 0% /dev tmpfs 100M 1.7M 98M 2% /run /dev/sda1 8.3G 980M 6.9G 13% / tmpfs 497M 0 497M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 497M 0 497M 0% /sys/fs/cgroup
On my case it's /dev/sda1.
Shutdown the VM from the host.
virsh shutdown my-vm
Resize the VM's image
qemu-img resize /var/lib/kvm/my-vm/my-vm.qcow2 +5G
Copy the VM's image
cp /var/lib/kvm/my-vm/my-vm.qcow2 /var/lib/kvm/my-vm/my-vm-original.qcow2
Increase the partition that you took note at the beginning
virt-resize --expand /dev/sda1 /var/lib/kvm/my-vm/my-vm-original.qcow2 /var/lib/kvm/my-vm/my-vm.qcow2
Note: to use virt-resize command you need package libguestfs-tools
Start the VM
virsh start my-vm
Check that your VM's partition increased
# df -h Filesystem Size Used Avail Use% Mounted on udev 479M 0 479M 0% /dev tmpfs 100M 1.7M 98M 2% /run /dev/sda1 14G 982M 13G 8% / tmpfs 497M 0 497M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 497M 0 497M 0% /sys/fs/cgroup
Method 2
Shutdown the VM from the host.
virsh shutdown my-vm
Resize the VM's image
qemu-img resize /var/lib/kvm/my-vm/my-vm.qcow2 +5G
Start the VM
virsh start my-vm
SSH to the VM and check what partition do you want to increase
# df -h Filesystem Size Used Avail Use% Mounted on udev 479M 0 479M 0% /dev tmpfs 100M 1.7M 98M 2% /run /dev/sda1 8.3G 980M 6.9G 13% / tmpfs 497M 0 497M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 497M 0 497M 0% /sys/fs/cgroup
In my case it is /dev/sda1. Running the next command you can see that /dev/sda has more space than the partitions are using
# fdisk -l Disk /dev/sda: 16 GiB, 17144217600 bytes, 33484800 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x91eb62c9 Device Boot Start End Sectors Size Id Type /dev/sda1 63 17931640 17931578 8.6G 83 Linux /dev/sda2 17934336 21932031 3997696 1.9G 82 Linux swap / Solaris
Delete partitions /dev/sda1 and /dev/sda2
Note: This will not delete/corrupt the files on this partition if it is recreated correctly. To correctly recreate a partition it needs to start at the same sector as before so take note of that from the above output, and end at a higher sector as we want to enlarge the partition.
fdisk -c=dos /dev/sda d 1 d 2 (this will be automatically selected as in my case at least, it was the last partition)
Recreate a larger /dev/sda1 partition
n p 1 63 (first sector of the new /dev/sda1 partition must be the same as before, so check what it was) +14G (replace 14 with what you want the full size of the partition to be)
Check that partition /dev/sda1 has been created correctly and take a note of the last sector
p Disk /dev/sda: 16 GiB, 17144217600 bytes, 33484800 sectors Geometry: 4 heads, 32 sectors/track, 2084 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x91eb62c9 Device Boot Start End Sectors Size Id Type /dev/sda1 63 29360191 29360129 14G 83 Linux
Recreate the SWAP partition
n p 2 29362887 (leave some free sectors between partitions; I left the same amount as before: 2696) <press enter> (it will default to the last sector -1) t 2 82 (this will change the partition to SWAP)
Check that the partitions have been correctly recreated
p Disk /dev/sda: 16 GiB, 17144217600 bytes, 33484800 sectors Geometry: 4 heads, 32 sectors/track, 2084 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x91eb62c9 Device Boot Start End Sectors Size Id Type /dev/sda1 63 29360191 29360129 14G 83 Linux /dev/sda2 29362887 33484799 4121913 2G 82 Linux swap / Solaris
Write the changes and quit
w
Reboot the VM to make the kernel read the new partition table.
virsh reboot my-vm
SSH to the VM and run
resize2fs /dev/sda1
Check that the partition has increased
df -h
Format and activate the new SWAP partition
mkswap /dev/sda2 swapon /dev/sda2
Copy the new UUID and replace the old one in /etc/fstab so it is available after a reboot.
Check that it is available
free -m
Increase the size of a VM's disk for LVM groups
Shutdown the VM from the host:
virsh shutdown my-vm
Resize the VM's image:
qemu-img resize /var/lib/kvm/my-vm/my-vm.qcow2 +5G
Start the VM
virsh start my-vm
Create a new partition with fdisk. Note: Be careful what sectors do you choose for the partition start - end. You could check the free sectors with fdisk -l /dev/vda
fdisk /dev/vda
Welcome to fdisk (util-linux 2.31.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): n
Partition type
p primary (1 primary, 1 extended, 2 free)
l logical (numbered from 5)
Select (default p): p
Partition number (3,4, default 3):
First sector (487424-65011711, default 487424): 23066630
Last sector, +sectors or +size{K,M,G,T,P} (23066630-65011711, default 65011711):
Created a new partition 3 of type 'Linux' and of size 20 GiB.
Command (m for help): t
Partition number (1-3,5, default 5): 3
Hex code (type L to list all codes): 8e
Changed type of partition 'Linux' to 'Linux LVM'.
Command (m for help): w
The partition table has been altered.
Syncing disks.
create new PV (Physical Volume)
pvcreate /dev/vda3
Add the newly created partition to Volume group:
sudo vgextend test-vg /dev/vda3
Extend the LV to the to the requested size or to full extend:
lvextend -L+6G /dev/test-vg/root lvextend -l +100%FREE /dev/test-vg/root
Run the following command to have the new space recognized:
resize2fs /dev/test-vg/root
