Re: [vnrg] Logical vs. virtual

[Roland Bless <roland.bless at kit.edu>]

Hi,

On 11.02.2011 16:59, Roland Bless wrote:
> the difference between logical and virtual isn't
> that easy and sometimes seems artificial.

After spending some more thoughts on this:
it seems to be the case that both mechanisms are often combined
and that they can be applied on top of each other in various ways:
consider some kind of Ethernet link aggregation mechanism that probably
provides mainly a logical resource, but on top of this logical
link one could provide a virtual link, whose interface
looks exactly like an ordinary Ethernet link (except for
higher capacity, higher resilience etc.) between a single
pair of MAC addresses.
So that explains, why the distinction between logical
and virtual is often unclear or blurred.

> * a virtual resource appears to a user of that resource
>   as if he is the (exclusive) owner of that resource.
>   A user's access is always carried out on the real resource.

> * a logical resource is created by transforming one
>   or several features of a real resource and by
>   offering it in this way to the user.
> 
> This requires use of a mapping layer that transforms
> the interface of the real resource(s) into a more
> purposeful interface. Thus, the logical resource/device
> may be simpler to handle from a user's point of view
> and constitutes an improved but different resource
> or device.

Such transformations may be performed in order to:
change the size of transport units, change the capacity,
change the access delay, change the access mode, combine
several devices, distribute to several devices, etc.

Regards,
 Roland