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1.2.7. Converting an image to RAW format

Red Hat Ceph can store, but does not support using, QCOW2 images to host virtual machine (VM) disks.

When you upload a QCOW2 image and create a VM from it, the compute node downloads the image, converts the image to RAW, and uploads it back into Ceph, which can then use it. This process affects the time it takes to create VMs, especially during parallel VM creation.

For example, when you create multiple VMs simultaneously, uploading the converted image to the Ceph cluster might impact already running workloads. The upload process can starve those workloads of IOPS and impede storage responsiveness.

To boot VMs in Ceph more efficiently (ephemeral back end or boot from volume), the Image service image format must be RAW.

Procedure

  1. Converting an image to RAW might yield an image that is larger in size than the original QCOW2 image file. Run the following command before the conversion to determine the final RAW image size: 

    qemu-img info <image>.qcow2

  2. Convert an image from QCOW2 to RAW format: 

    qemu-img convert -p -f qcow2 -O raw <original_qcow2_image>.qcow2 <new_raw_image>.raw

1.2.7.1. Configuring the Image service to accept only RAW and ISO

You can configure the Image service to accept only RAW and ISO image formats.

Procedure

  1. Add an additional environment file that contains the following content in the openstack overcloud deploy command with your other environment files: 

    parameter_defaults:
  ExtraConfig:
    glance::config::api_config:
      image_format/disk_formats:
        value: "raw,iso"