[Openstack-operators] what is the different in use Qcow2 or Raw in Ceph
openstack at medberry.net
Thu May 28 14:36:52 UTC 2015
This isn't remotely related to btrfs. It works fine with XFS. Not sure how
that works in Fuel, never used it.
On Thu, May 28, 2015 at 8:01 AM, Forrest Flagg <fostro.flagg at gmail.com>
> 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>
>>>> 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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