Re: [Xen-devel] Virtualization project idea

[Michal Novotny <minovotn@xxxxxxxxxx>]

On 08/27/2010 03:08 PM, Pasi Kärkkäinen wrote:
> On Fri, Aug 27, 2010 at 06:33:35PM +0530, Dhananjay Goel wrote:
>    
> >     Yes, exactly. So, we wanted to know if it is possible to *share USB*
> >     across VMs.
> >
> >      
> I don't think USB protocol has been designed for *sharing*.
> I'm pretty certain only one computer/device/VM can use USB device at a time.
>
> -- Pasi
>
>    
Pasi, I agree. I think the think here is that Dhananjay confused the USB 
device sharing with the file system sharing. I guess the USB protocol 
was not designed for sharing nevertheless sharing the filesystem on a 
USB stick is a completely different think.
Dhananajay, you need to plug in the USB stick onto one computer (and 
it's impossible to plug it into multiple computer at one time, of 
course) and then setup the sharing. Everybody here is talking about the 
hardware abstraction and virtualization and what you wrote is a 
completely different thing - it's software-related and this has nothing 
to do with the hardware emulation/abstraction what-so-ever.
Considering the NFS and all the sharing protocols there was something 
why it doesn't corrupt the data. I'm no expert on this subject but I 
think this is because they run in the server-client mode. All the 
clients are talking to the server and the server itself is one computer 
that's having the just one operating system working with this particular 
device - no matter what the underlaying device is - it may be everything 
- USB stick, IDE/SCSI/SAS drive or just a relay workstation to save all 
the data into one remote media (e.g. for replication). What I mean is 
that the basic thing is that it's running on only one operating system 
(because of it's connected to this one machine *only*) so it takes care 
of everything and it's aware of the write-cache and data operations 
being done to this media.
Michal

--
Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat


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