Mar 14, 2018#Tutorial #Virtual Machine #qcow2 #KVM

How to shrink qcow2 file (LVM Logical Volume Manager, XFS file system)?

First we need to shrink the partition, and then shrink the qcow2 file.Guestdf -h centos_7_df

Let's get more information before we proceed.vgdisplay pvdisplay centos_7_vgdisplay_pvdisplay

It tells us the volume group name, total allocated size, free size, and physical volume name.

Name

Value

Volume group name

centos_learn

Physical volume name

/dev/vda2

Allocated size

103.75G

Free size

7.25G

Let's get information on physical disk.fdisk -l centos_7_fdisk

The physical disk size /dev/vda is 120.3G.Let's review our situation. We want to shrink /dev/vda to 80G. In order to do that, we need to shrink /home volume from 50G to 10G.Resize homeCentos use XFS file system which cannot resize. To workaround this, we need to remove and create an new one.

Backup the content in /home, either using rsync or tar

Rsync
```
rsync -avP /home/ /root/home
```
Tar
```
tar -czvf /root/home.tar.gz -C /home .
```

Unmount home

umount /dev/mapper/centos_learn-home

Remove home logical volume

lvremove /dev/mapper/centos_learn-home

Create an new home logical volume

lvcreate -L 10G -n home centos_learn

Format home logical volume to XFS file system

mkfs.xfs /dev/centos_learn/home

Mount home

mount /dev/mapper/centos_learn-home

Restore the content in home

Rsync
```
rsync -avP /root/home/ /home
```
Tar
```
tar -xf /root/home.tar.gz -C /home
```

Reduce volume group size

Check segments

pvs -v --segments /dev/vda2

centos_7_segments

We want free space all the way at the end. In order to do that, we need to move other data above free space.

In our situation, we need to move root logical volume.

pvmove --alloc anywhere /dev/vda2:13760-26559

Reduce the size

First we need to do a test

pvresize -tv --setphysicalvolumesize 60G /dev/vda2

Reduce the size, if there is no error from testing

pvresize -v --setphysicalvolumesize 60G /dev/vda2

Verifyvgdisplay pvdisplayShutdownResize qcow2 file requires the guest to be shutdown.shutdown -h nowHostInstall virt-filesystems.yum -y install libguestfs-tools-cCheck qcow2 file systemvirt-filesystems --long --parts --blkdevs -h -a vm_learn.qcow2

Currently, the virtual size of our qcow2 is 112G. We want to shrink it to 80G.

Create output disk

truncate -s 80G vm_learn_new.qcow2

Shrink /dev/sda2

virt-resize --output-format qcow2 --shrink /dev/sda2 vm_learn.qcow2 vm_learn_new.qcow2

FinallyEdit guest to use the newly created qcow2 disk file.virsh edit vm_learnMake sure everything works before deleting the old disk.

Mike MaiBrooklyn, NY

I am full-stack web developer, passionate about building world class web applications. Knowledge in designing, coding, testing, and debugging. I love to solve problems.