[one-users] Ceph and thin provision

[Kenneth]

I haven't tested much on non-persistent image as I have no use on
them unless on experiments. Also, I haven't tried any volatile image,
sorry. 

_A not persistent image is writeable?_ 

Short answer: NO


Long answer: Yes, sort of. When you instantiate a non persistent
image, nebula create a "another disk" in the background temporarily. You
can check that on when you issue "rbd ls -p one". You'll see something
like this. 

one-34 -------> this is the non persistent image
disk
one-34-73-0 --------> this is the "temporary clone" of the disk
when you instantiate a VM
one-34-80-0 ---------> another VM which uses
the non persistent image one-34 

This is why you can instantiate two or
more VMs using a non-persistent image. If I'm not mistaken, the
temporary disk will be destoyed once you shutdown the VM from nebula
sunstone. But as long as the VM is running, the data is there. You can
even reboot the VM with non-persistent disk and still have data. You
lose the data once Nebula destroys VM disk, that is, when you SHUTDOWN
or DELETE the VM from nebula sunstone. 

As for thick and thin
provision, all of my images in ceph are thick, because my base image is
25 GB disk from a KVM template and then I imported it in ceph (it was
converted from qcow2 to rbd). It consumes whole 25GB on my ceph storage.
I just clone that "template image" every time I deploy a new VM. 

I
haven't tried creating a thin or thick provision in ceph rbd from
scratch. So basically, I can say that a 100GB disk will consume 100GB
RBD in ceph (of course it will be 200GB in ceph storage since ceph
duplicates the disks by default). 
---

Thanks,
Kenneth
Apollo Global
Corp.

On 12/12/2013 04:52 PM, Mario Giammarco wrote: 

> In several
virtualization systems you can have a virtual disk drive:
> 
> -thick,
so a thick disk of 100gb uses 100gb of space; -thin, so a thin disk of
100gb uses 0gb when empty and starts using space when the virtual
machine fills it.
> 
> So I can have a real hdd of 250gb with inside ten
virtual thin disks of 1000gb each, if they are almost empty. 
> I have
checked again and ceph rbd are "thin". 
> 
> BTW: I thank you for you
explanation of persistent/not persistent, I was not able to find it in
docs. Can you explain me also what a "volatile disk" is? 
> A not
persistent image is writeable? When you reboot a vm with a not
persistent image you lose all datda written to it?
> 
> Thanks again,
>
Mario 
> 
> 2013/12/12 Kenneth <kenneth at apolloglobal.net>
> 
>> Hi, 
>>

>> Can you elaborate more on what you want to achieve? 
>> 
>> If you
have a 100GB image and it is set to persistent, you can instantiate that
image immediately and deploy/live migrate it to any nebula node. Only
one running instance of VM of this image is allowed. 
>> 
>> If it is a
100GB non persistent image, you'll have to wait for ceph to "create a
copy" of it once you deploy it. But you can use this image multiple
times simutaneously. 
>> ---
>> 
>> Thanks,
>> Kenneth
>> Apollo Global
Corp.
>> 
>> On 12/11/2013 07:28 PM, Mario Giammarco wrote: 
>> 
>>>
Hello, I am using ceph with opennebula. I have created a 100gb disk
image and I do not understand if it is thin or thick.
>>> 
>>> I hope I
can have thin provision.
>>> 
>>> Thanks,
>>> Mario 
>>> 
>>>
_______________________________________________
>>> Users mailing
list
>>> Users at lists.opennebula.org
>>>
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