[one-users] Few issues / concern about detach/attach operation of VM disks

[Carlos Martín Sánchez]

Hi,

On Wed, Jan 15, 2014 at 2:08 PM, kiran ranjane <kiran.ranjane at gmail.com>
 wrote:

> Hello,
>
> Scenario :
>
> -- I created a VM from a template which had 2 disk (OS, Datablock).
> -- The VM was deployed properly in Running State and after that I tried
> the detach operation on Datablock disk. The disk was detached correctly
> without any errors but I want to attach the same disk again to the VM and
> there is no such way to do it in ONE.
>

If the disk was volatile, it is lost. But if the disk was using an image,
you can attach that same image again. So I'd say that the use case is
supported, you just have to make sure that disks that may be used later
need to be backed by Images.

-- The disk that are listed below in Storage tab under VM should be there
> even after you detach the disk from the VM so that in case we need it back
> we can attach the same disk again.
>

This can be useful in some cases, but I'm not sure it is desirable in all
situations. If the disk is using a persistent Image, I'd expect that image
to be released, and ready to be used for another VM, as soon as the disk is
detached.

-- Also we should have the option to move/attach the data-disk of a
> particular VM to any other VM.
>

It is possible, if the disk is backed by an Image. You can detach + detach
to the other VM.


> -- Now if I detach the disk the data that is stored in that particular
> disk is gone. Is there a way to get it back?
>

If it was a volatile disk, it was deleted when it was detached.


Maybe the requirement to manage persistency with Images is not intuitive,
but it is the OpenNebula model. First you define the storage, and then you
use it in the VMs.

The only thing missing to fully support your use case may be a similar
operation to detach, but less definitive. Maybe an "unmount" action could
detach the disk without touching the files. I don't how useful it would be,
since it can be done from the guest. What do you think of this?

Best regards
--
Carlos Martín, MSc
Project Engineer
OpenNebula - Flexible Enterprise Cloud Made Simple
www.OpenNebula.org | cmartin at opennebula.org |
@OpenNebula<http://twitter.com/opennebula><cmartin at opennebula.org>
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