Re: [Xen-users] VM accessing Hosts hard disk

["M.A. Williamson" <maw48@xxxxxxxxx>]

On Dec 24 2006, Thomas Miller wrote:

> Andrew McGregor wrote:
> > Thomas Miller wrote:
> > > I want to be able to have a shared drive that the VMs can access from 
> > > the host machine.
> > > Basically I have downloaded install files from the internet into a 
> > > directory on the host and would like to copy them to the VM to run vs 
> > > re-downloading them from the internet.
> > > Thanks for pointing me in the right direction.
> > Samba?  FTP?  scp?  Just pick any network service - not really a Xen 
> > issue.
> I am really new to all this stuff and wasn't sure if there was a trick 
> way with Xen or some standard method.  I will probably use Samba as I 
> have that already set up.  Thanks all of you.
Didn't get round to responding to this earlier, but thought I'd add my 
$0.02 worth...
When doing any kind of communication between two domains, it's almost 
always appropriate to think of them as being two separate machines. As a 
result, you generally share files in the same way as with separate servers. 
The three main approaches of this type being:
1) scp ;-) 2) use some kind of network block device and a cluster 
filesystem [in the Xen case, you might also share the same block device 
directly, to avoid the overhead of virtual network] 3) network filesystem - 
usually NFS or Samba
Direct sharing of disk drives can be an option, but sharing block-level 
drives without using a cluster filesystem can easily cause upsets. You can 
have multiple read-only users of a block device, or a lone writeable user. 
You can't mix readers and writers at the same time (it confuses the 
readers) and you certainlycan't have multiple writers (it trashes the FS). 
Careful read-only exporting of block devices, and careful use of the mount 
command can help to prevent you from breaking things if you go down this 
route...
Finally, there's my pet project: XenFS. This behaves to the user much like 
NFS, but is implemented to use Xen's shared memory protocols directly, 
instead of using the virtual network. I imagine this is the kind of thing 
you might have had in mind when you asked your original question ;-) XenFS 
is a long way off being stable though, so unless you like to play with 
hairy code I'd recommend you stick with your network filesystem approach 
:-)
Sorry for rambling, it's getting late!

Cheers,
Mark

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