[Openstack-operators] what is the different in use Qcow2 or Raw in Ceph
fostro.flagg at gmail.com
Thu May 28 14:01:44 UTC 2015
I'm also curious about this. Here are some other pieces of information
relevant to the discussion. Maybe someone here can clear this up for me as
well. The documentation for Fuel 6.0, not sure what they changed for 6.1,
 states that when using Ceph one should disable qcow2 so that images are
stored in raw format. This is due to the fact that Ceph includes its own
mechanisms for copy-on-write and snapshots. According to the Ceph
documentation , this is true only when using a BTRFS file system, but in
Fuel 6.0 Ceph uses XFS which doesn't provide this functionality. Also, 
recommends not using BTRFS for production as it isn't considered fully
mature. In addition, Fuel 6.0  states that OpenStack with raw images
doesn't support snapshotting.
Given this, why does Fuel suggest not using qcow2 with Ceph? How can Ceph
be useful if snapshotting isn't an option with raw images and qcow2 isn't
recommended? Are there other factors to take into consideration that I'm
On Thu, May 28, 2015 at 8:02 AM, David Medberry <openstack at medberry.net>
> and better explained here:
> On Thu, May 28, 2015 at 6:02 AM, David Medberry <openstack at medberry.net>
>> The primary difference is the ability for CEPH to make zero byte copies.
>> When you use qcow2, ceph must actually create a complete copy instead of a
>> zero byte copy as it cannot do its own copy-on-write tricks with a qcow2
>> So, yes, it will work fine with qcow2 images but it won't be as
>> performant as it is with RAW. Also, it will actually use more of the native
>> underlying storage.
>> This is also shown as an Important Note in the CEPH docs:
>> On Thu, May 28, 2015 at 4:12 AM, Shake Chen <shake.chen at gmail.com> wrote:
>>> Now I try to use Fuel 6.1 deploy openstack Juno, use Ceph as cinder,
>>> nova and glance backend.
>>> In Fuel document suggest if use ceph, suggest use RAW format image.
>>> but if I upload qcow2 image, seem working well.
>>> what is the different use qcow2 and RAW in Ceph?
>>> Shake Chen
>>> OpenStack-operators mailing list
>>> OpenStack-operators at lists.openstack.org
> OpenStack-operators mailing list
> OpenStack-operators at lists.openstack.org
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