Re: Thick provisioning

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Hi all,

Thanks for the replies.

The main reason why I was looking for the thin/thick provisioning setting
is that I want to be sure that provisioned space should not exceed the
cluster capacity.

With thin provisioning there is a risk that more space is provisioned than
the cluster capacity. When you monitor closely the real usage, this should
not be a problem; but from experience when there is no hard limit,
overprovisioning will happen at some point.

Sinan

> I can only speak for some environments, but sometimes, you would want to
> make sure that a cluster cannot fill up until you can add more capacity.
>
> Some organizations are unable to purchase new capacity rapidly and making
> sure you cannot exceed your current capacity, then you can't run into
> problems.
>
> It may also come from an understanding that thick provisioning will
> provide
> more performance initially like virtual machines environment.
>
> Having said all of this, isn't there a way to make sure the cluster can
> accommodate the size of all RBD images that are created. And ensure they
> have the space available? Some service availability might depend on making
> sure the storage can provide the necessary capacity.
>
> I'm assuming that this is all from an understanding that it is more costly
> to run such type of environments, however, you can also guarantee that you
> will never fill up unexpectedly your cluster.
>
> Sam
>
> On Oct 18, 2017 02:20, "Wido den Hollander" <wido@xxxxxxxx> wrote:
>
>
>> Op 17 oktober 2017 om 19:38 schreef Jason Dillaman
>> <jdillama@xxxxxxxxxx>:
>>
>>
>> There is no existing option to thick provision images within RBD. When
>> an image is created or cloned, the only actions that occur are some
>> small metadata updates to describe the image. This allows image
>> creation to be a quick, constant time operation regardless of the
>> image size. To thick provision the entire image would require writing
>> data to the entire image and ensuring discard support is disabled to
>> prevent the OS from releasing space back (and thus re-sparsifying the
>> image).
>>
>
> Indeed. It makes me wonder why anybody would want it. It will:
>
> - Impact recovery performance
> - Impact scrubbing performance
> - Utilize more space then needed
>
> Why would you want to do this Sinan?
>
> Wido
>
>> On Mon, Oct 16, 2017 at 10:49 AM,  <sinan@xxxxxxxx> wrote:
>> > Hi,
>> >
>> > I have deployed a Ceph cluster (Jewel). By default all block devices
> that
>> > are created are thin provisioned.
>> >
>> > Is it possible to change this setting? I would like to have that all
>> > created block devices are thick provisioned.
>> >
>> > In front of the Ceph cluster, I am running Openstack.
>> >
>> > Thanks!
>> >
>> > Sinan
>> >
>> > _______________________________________________
>> > ceph-users mailing list
>> > ceph-users@xxxxxxxxxxxxxx
>> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>>
>>
>>
>> --
>> Jason
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