Daniel P. Berrangé
2021-Jan-06 15:48 UTC
[ovirt-devel] Issue: Device path changed after adding disks to guest VM
On Wed, Jan 06, 2021 at 04:36:46PM +0100, Peter Krempa wrote:> On Wed, Jan 06, 2021 at 17:16:24 +0200, Nir Soffer wrote: > > On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li at gmail.com> wrote: > > [...] > > > Comparing to state before reboot: > > > > # virsh -r domblklist disk-mapping > > Target Source > > --------------------------------------------------------------------------------------------------------------------------------------------------------------- > > sdc - > > sda /rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5 > > vda /dev/mapper/3600140594af345ed76d42058f2b1a454 > > vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5 > > vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef > > > > # ls -lh /dev/disk/by-id/virtio-* > > lrwxrwxrwx. 1 root root 9 Jan 6 09:42 > > /dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda > > lrwxrwxrwx. 1 root root 9 Jan 6 09:42 > > /dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb > > lrwxrwxrwx. 1 root root 9 Jan 6 09:51 > > /dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc > > > > In the guest disks are mapped to the same device name. > > > > It looks like libivrt domblklist is not correct - vdb and vdc are switched. > > Peter, this expected? > > The names in 'virsh domblklist' are unfortunately and confusingly chosen > to match the expected /dev/ device node name, but it's at kernel's > discretion to name /dev/ nodes. > > This means that it's not guaranteed that what you see in 'virsh > domblklist' will match the state in the guest.Essentially the only thing the disk device name is used for is sorting the <disk> elements within the XML document. This in turn affects what order PCI addresses (virtio-blk) or SCSI LUNS (virtio-scsi) are assigned in. This influences/hints as to what order the guest OS *might* assign device names in. The device name from the XML is not exposed to the guest directly though. Certainly when hotplugging/unplugging is involved all bets are off wrt what disk names you'll see in the guest vs the XML. Dont expect them to match except by luck. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
I am doing a 2 year retraining at the moment to become a system admin. There are 2 weeks of HyperV on the schedule (sadly the only virtualization that will be taught in that course) in august and plan to sneak out of class during that time to to something useful and get a grip on the kvm/qemu/libvirt side of the VM cake (class is completely online, so the sneaking out is doable). Can anybody recommend good online learning resources for someone with yet quite foggy basic understanding of things? thanks and best Gunnar