[one-users] Storage subsystem: which one?

[Humberto N. Castejon Martinez]

Hi,

Thank you very much, Fabian and Carlos, for your help. Things are much more
clear now, I think.

*Sharing the image repository.
If I understood right, the aim with sharing the image repository between the
front-end and the workers is to increase performance  by reducing (or
eliminating) the time needed to transfer an image from the repository to the
worker that will run an instance of such image. I have, however, a
question/remark here. To really reduce or eliminate the transfer time, the
image should already reside on the worker node or close to it. If the image
resides on a central server (case of NFS, if I am not wrong) or on an
external shared distributed storage space (case of MooseFS, GlusterFS,
Lustre, and the like), there is still a need to transfer the image to the
worker, right? In the case of a distributed storage solution like MooseFs,
etc., the worker could itself be part of the distributed storage space. In
that case, the image may already reside on the worker, although not
necessarily, right? But using the worker as both a storage server and client
may actually compromise performance, for what I have read.
Am I totally wrong with my thoughts here? If not, do we really increase
transfer performance by sharing the image repository using, e.g. NFS? Are
there any performance numbers for the different cases that could be shared?

* Sharing the <VM_dir>.
Sharing the <VM_dir> between the front-end and the workers is not really
needed, but it is more of a convenient solution, right?
Sharing the <VM_dir> between the workers  themselves might be needed for
live migration. I say "might" because i have just seen that, for example,
with KVM we may perform live migrations without a shared storage [2]. Has
anyone experimented with this?

Regarding the documentation, Carlos, it looks fine. I would only suggest the
possibility of documenting the 3rd case where the image repository is not
shared but the <VM_dir> is shared.

Thanks!

Cheers,
Humberto

[1]
http://opennebula.org/documentation:rel3.0:sfs#considerations_limitations
[2] http://www.mail-archive.com/libvir-list@redhat.com/msg23674.html


Date: Mon, 17 Oct 2011 16:30:13 +0200
From: Fabian Wenk <fabian at wenks.ch>
To: users at lists.opennebula.org
Subject: Re: [one-users] Storage subsystem: which one?
Message-ID: <4E9C3BF5.1060900 at wenks.ch>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hello Carlos

On 17.10.2011 11:34, Carlos Mart?n S?nchez wrote:
> Thank you for your great contributions to the list!

You're welcome.

> I'd like to add that we tried to summarize the implications of the shared
> [1] and non-shared [2] approaches in the documentation, let us know if
there
> are any big gaps we forgot about.

Thank you for documenting it on the website. I think it is
complete and mentions all important facts about the two storage
possibilities.


bye
Fabian
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