[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: [Xen-devel] Re: Questions on Copy-on-Write

  • To: "Christian Limpach" <chris@xxxxxx>
  • From: "Williamson, Mark A" <mark.a.williamson@xxxxxxxxx>
  • Date: Mon, 2 Feb 2004 14:36:32 -0000
  • Cc: "Devel Xen" <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 03 Feb 2004 23:32:25 +0000
  • List-id: List for Xen developers <xen-devel.lists.sourceforge.net>
  • Thread-index: AcPpk3QGpMqcosnxRTOkP/wq56OaRAAA/nkA
  • Thread-topic: [Xen-devel] Re: Questions on Copy-on-Write

> Doesn't this sit at the wrong level?  This would make all 
> disk accesses on
> these devices go through Domain0?

That's not quite right: virtual block devices are an abstraction
provided by Xen and domains that use them talk to Xen directly, without
going through Dom0.  VBDs are a way of securely sharing portions of the
physical disk space in the system between domains - Dom0 creates VBDs to
tell Xen what domains can access what parts of the disk.  Those domains
then talk to Xen directly to access those areas.

A domain could be given read only access to the VBD with a "standard
image" for all domains on it and read-write access to another VBD for
it's own personal use.  Using Bin's CoW driver, the domain can then
store all its updates to the standard image in the read-write VBD.  The
domain then talks directly to Xen in order to access these VBDs, same as



The SF.Net email is sponsored by EclipseCon 2004
Premiere Conference on Open Tools Development and Integration
See the breadth of Eclipse activity. February 3-5 in Anaheim, CA.
Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.