Image Volume Cache not working for RAW images - openstack

Question

The image volume cache is only working for a QCOW2 image and not for a RAW image. This feature of Cinder promises to improve the volume creation performance drastically.
https://docs.openstack.org/cinder/latest/admin/blockstorage-image-volume-cache.html

Answer 1

Create volume from the image, first try to call clone_image interface, then try to call clone_image_volume interface, and then try and use the image cache. If all else fails, fall back to default behavior of creating volume　download the image data and copy it into the volume.
If volume backend is ceph and RAW image also in ceph, create volume from a RAW image, will clone image directly in ceph, and not use the image cache.
#utils.retry(exception.SnapshotLimitReached, retries=1)
def _create_from_image(self, context, volume,
image_location, image_id, image_meta,
image_service, **kwargs):
LOG.debug("Cloning %(volume_id)s from image %(image_id)s "
" at location %(image_location)s.",
{'volume_id': volume.id,
'image_location': image_location, 'image_id': image_id})
virtual_size = image_meta.get('virtual_size')
if virtual_size:
virtual_size = image_utils.check_virtual_size(virtual_size,
volume.size,
image_id)
# Create the volume from an image.
#
# First see if the driver can clone the image directly.
#
# NOTE (singn): two params need to be returned
# dict containing provider_location for cloned volume
# and clone status.
# NOTE (lixiaoy1): Currently all images are raw data, we can't
# use clone_image to copy data if new volume is encrypted.
volume_is_encrypted = volume.encryption_key_id is not None
cloned = False
model_update = None
if not volume_is_encrypted:
model_update, cloned = self.driver.clone_image(context,
volume,
image_location,
image_meta,
image_service)
# Try and clone the image if we have it set as a glance location.
if not cloned and 'cinder' in CONF.allowed_direct_url_schemes:
model_update, cloned = self._clone_image_volume(context,
volume,
image_location,
image_meta)
# If we're going to try using the image cache then prepare the cache
# entry. Note: encrypted volume images are not cached.
if not cloned and self.image_volume_cache and not volume_is_encrypted:
# If _prepare_image_cache_entry() has to create the cache entry
# then it will also create the volume. But if the volume image
# is already in the cache then it returns (None, False), and
# _create_from_image_cache_or_download() will use the cache.
model_update, cloned = self._prepare_image_cache_entry(
context,
volume,
image_location,
image_id,
image_meta,
image_service)
# Try and use the image cache, and download if not cached.
if not cloned:
model_update = self._create_from_image_cache_or_download(
context,
volume,
image_location,
image_id,
image_meta,
image_service)
self._handle_bootable_volume_glance_meta(context, volume,
image_id=image_id,
image_meta=image_meta)
return model_update
https://github.com/openstack/cinder/blob/master/cinder/volume/flows/manager/create_volume.py