Cole Robinson wrote: > Michael DeHaan wrote: >> Cole Robinson wrote: >>> Michael DeHaan wrote: >>> >>>> Chris Lalancette wrote: >>>> >>>>> Michael DeHaan wrote: >>>>> >>>>> >>>>>> I had a user question about how they can specify blktap for Xen in >>>>>> Cobbler instead of the file driver (for performance reasons) ... well, >>>>>> it turns out they can't (yet). >>>>>> >>>>>> Under what conditions can we use blktap, and is that advisable? (I had >>>>>> thought this might work like virtio, in which case, passing in the os >>>>>> version uses a table, but it seems this may only actually depend on the >>>>>> host and has no guest limitations?) >>>>>> >>>>>> >>>>> That's exactly right. It's a property of how the host OS accesses the disk on >>>>> behalf of the domain, not of how the disk is presented to the domain. In fact, >>>>> for Xen PV domains, you should *only* ever use blktap (i.e. tap:aio:); direct >>>>> file: access can corrupt your guest domains on host crash. The situation with >>>>> FV domains is more complicated, but there, you can use file:, since it properly >>>>> does flushing. >>>>> >>>>> >>>>> >>>> >>>>>> It looks like from the virtinst code I could just call >>>>>> utils.is_blktap_capable() from my libvirt-using application and if so, >>>>>> then pass the driver=DRIVER_TAP options to virstinst. >>>>>> >>>>>> Good idea? Bad idea? >>>>>> >>>>>> >>>>> The only reasonable default for Xen PV domains, in my opinion. >>>>> >>>>> >>>>> >>>> Thanks. >>>> >>>> FWIW the default behavior of python-virtinst seems to be to /not/ use >>>> blktap, and should probably be fixed then if there's a potential >>>> corruption problem. >>>> >>>> I haven't tested command line virt-install to see what it does. >>>> >>>> >>> That default is actually set in virt-install and virt-manager, but >>> probably should have been moved into the virtinst library a long time ago. >>> >>> - COle >>> >> Yeah, I can't keep up very well when stuff doesn't happen there :) >> >> Should I make the fix in koan also or do you want to move it? >> >> --Michael >> > > I'll take a look at moving it into the library, but for back compat it > wouldn't hurt to set the default in koan. The virt-install code is: > > http://hg.et.redhat.com/cgi-bin/hg-virt.cgi/applications/virtinst--devel/file/5d6dc8af58b5/virt-install#l209 > This is now upstream: we will set the 'tap' default if installing a PV guest: http://hg.et.redhat.com/cgi-bin/hg-virt.cgi/applications/virtinst--devel/rev/ab66c26436cf If creating a standalone VirtualDisk instance though, the default won't be set, since we don't know what type of guest it will be attached to. - Cole _______________________________________________ et-mgmt-tools mailing list et-mgmt-tools@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/et-mgmt-tools
