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, [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 [2], 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, [2] recommends not using BTRFS for production as it isn't considered fully mature. In addition, Fuel 6.0 [3] 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 missing? [1] https://docs.mirantis.com/openstack/fuel/fuel-6.0/terminology.html#qcow2 [2] http://ceph.com/docs/master/rados/configuration/filesystem-recommendations/ [3] https://docs.mirantis.com/openstack/fuel/fuel-6.0/user-guide.html#qcow-format-ug Thanks, Forrest On Thu, May 28, 2015 at 8:02 AM, David Medberry <openst...@medberry.net> wrote: > and better explained here: > http://ceph.com/docs/master/rbd/qemu-rbd/ > > On Thu, May 28, 2015 at 6:02 AM, David Medberry <openst...@medberry.net> > wrote: > >> 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 >> image. >> >> 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: >> http://ceph.com/docs/master/rbd/rbd-openstack/ >> >> On Thu, May 28, 2015 at 4:12 AM, Shake Chen <shake.c...@gmail.com> wrote: >> >>> Hi >>> >>> 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@lists.openstack.org >>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators >>> >>> >> > > _______________________________________________ > OpenStack-operators mailing list > OpenStack-operators@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators > >
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