This is a only version
Found at: raymii.org:70/KVM_convert_qcow2_disk_images_to_raw_disk_images_for_performance.txt
This is a text-only version of the following page on https://raymii.org:
Title : KVM convert qcow2 disk images to raw disk images for performance
Author : Remy van Elst
Date : 16-02-2014
URL : https://raymii.org/s/tutorials/KVM_convert_qcow2_disk_images_to_raw_disk_images_for_performance.html
Format : Markdown/HTML
This tutorial shows you how to convert KVM qcow2 disk images to raw disk images.
The qcow2 disk format has some decent features like encryption, compression and
copy to write support. However, the compression and the copy processes make it
quite a bit slower than raw disk images. Sometimes you want to convert the disk
images so that the VM will perform better.
I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!
Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.
You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days.
For me it has a performance boost. Using a RAID 1 setup with two 5900 RPM disks
and the `deadline` on the host and the `noop` scheduler without caching on a raw
image in the guest resulted in a boost over the default `deadline` scheduler on
a qcow2 image on the guest:
dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
Default Ubuntu 12.04 vmbuilder created vm on a qcow2 image without caching and
with the deadline scheduler in the VM:
1073741824 bytes (1.1 GB) copied, 658.396 s, 1.6 MB/s
The same VM, disk image converted to raw image without caching and using the
noop scheduler in the VM:
1073741824 bytes (1.1 GB) copied, 13.646 s, 78.7 MB/s
That's quite a performance boost. The KVM host has the following result with the
1073741824 bytes (1.1 GB) copied, 10.4034 s, 103 MB/s
### Converting the image
I'll convert the disk image for the example vm `vm1`. Change the name and disk
paths for your setup.
First shut down the VM:
virsh shutdown vm1
Then convert all the disk images using this command for each disk image:
qemu-img convert /var/lib/libvirt/images/vm1/ubuntu-kvm/tmp20ePgc.qcow2 /var/lib/libvirt/images/vm1/ubuntu-kvm/tmp20ePgc.raw
Edit the VM config:
virsh edit vm1
Change the `disk` section to point to the new raw image:
Change the lines `
` and `