On Tue, Nov 26, 2013 at 06:24:02PM +0800, Osier Yang wrote: > [[ TO libvir-list ]] > > Hi, Daniel, > > I'm going to share the thread to public list for further discussion. > Hope you > don't mind. > > On 26/11/13 02:37, Daniel Erez wrote: > >Hi Osier, > > > >It seems there's a limitation in libvirt that allows up to six disks in a > >virtio-scsi controller. I.e. when sending more than six disks, libvirt > >automatically creates a new controller but of type virtual LSI Logic SCSI. > >Is this behavior a known issue? > > For narrow SCSI bus, we allow 6 disks indeed. > > For wide SCSI bus, we allow 15 disks (not including the controller > itself on unit 7). > > I'm doubting if we have problem on detecting if it supports wide SCSI > bus though, since as far as I see from the user cases, it's always > narrow SCSI bus. > > >Shouldn't libvirt allow up to 256 disks > >per controller or at least create a new controller of type virtio-scsi when needed? > > The controller model for virtio-scsi controller is lsilogic, which we can't > change simply, since it might affect the existing guests. > > There was the similar discussion in libvir-list before [1]. > > But auto generation for controller is quite old, which I'm also not quite > clear about. I'd like see another discussion to make it more clear whether > we should do some work for upper layer app (e.g. oVirt). > > Basicly two points: > > * Should we do some changes on the maximum units for a SCSI controller, > I.e. Should 7 (narrow bus) 16 (wide bus) be changed to other numbers? > I'm afraid the changes could affect existing guests though. > > * Do we really want to put the burden on users, I.E, let them create the > controller explicitly. For use cases like one wants to add many > disks for > a guest, they need to know whether it's narrow SCSI bus or wide SCSI > bus first (which we don't expose outside), and then do the calculation > to know when to create a new SCSI controller. > > @Daniel, am I correct on your problems? Please comments if it doesn't > cover all your thoughts. The logic for auto-assignment of disks to controllers is never going to make everyone happy. If people really care about the mapping they should define it explicitly by providing a controller address with their disk XML. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list