Hi Devs,
Problem Statement: Performance and storage efficiency of shelving/unshelving
instance booted from image is far worse than instance booted from volume.
When you unshelve hundreds of instances at the same time, instance spawning
time varies and it mainly depends on the size of the instance snapshot and
the network speed between glance and nova servers.
If you have configured file store (shared storage) as a backend in Glance for
storing images/snapshots, then it's possible to improve the performance of
unshelve instance dramatically by configuring nova.image.download.FileTransfer
in nova. In this case, it simply copies the instance snapshot as if it is
stored on the local filesystem of the compute node. But then again in this
case, it is observed the network traffic between shared storage servers and
nova increases enormously resulting in slow spawning of the instances.
I would like to gather some thoughts about how we can improve the performance
of unshelve api (booted from image only) in terms of downloading large
size instance snapshots from glance.
I have proposed a nova-specs [1] to address this performance issue. Please take
a look at it.
During the last nova mid-cycle summit, Michael
Still<https://review.openstack.org/#/q/owner:mikal%2540stillhq.com+status:open,n,z>
has suggested alternative solutions to tackle this issue.
Storage solutions like ceph (Software based) and NetApp (Hardare based) support
exposing images from glance to nova-compute and cinder-volume with
copy in write feature. This way there will be no need to download the instance
snapshot and unshelve api will be pretty faster than getting it
from glance.
Do you think the above performance issue should be handled in the OpenStack
software as described in nova-specs [1] or storage solutions like
ceph/NetApp should be used in production environment? Apart from ceph/NetApp
solutions, are there any other options available in the market.
[1] https://review.openstack.org/#/c/135387/
Thank You,
Abhishek Kekane
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