Open Stack

Hi David,

So Ceph will use Copy-on-write even with XFS?

Thanks,

Steve

On Thu, May 28, 2015 at 10:36 AM, David Medberry <openstack at medberry.net>
wrote:

> 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>
> wrote:
>
>> 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 <openstack at 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 <openstack at 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.chen at 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 at lists.openstack.org
>>>>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
>>>>>
>>>>>
>>>>
>>>
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>>>
>>>
>>
>
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>


-- 
________________________________________________________________
 Steve Cousins             Supercomputer Engineer/Administrator
 Advanced Computing Group            University of Maine System
 244 Neville Hall (UMS Data Center)              (207) 561-3574
 Orono ME 04469                      steve.cousins at maine.edu
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