Public bug reported: Libvirt driver will attempt to connect the volume on the hipervisor twice for every volume provided to the instance when booting. If you examine the libvirt driver's spawn() method, both _get_guest_xml (by means of get_guest_storage_config) and _create_domain_and_network will call the _connect_volume method which works out the volume driver and then dispatches the connect logic.
This is especially bad in the iscsi volume driver case, where we do 2 rootwraped calls in the best case, one of which is the target rescan, that can in theory add and remove devices in the kernel. I suspect that fixing this will make a number of races that have to do with the volume not being present when expected on the hypervisor, at least less likely to happen, in addition to making the boot process with volumes more performant. An example of a race condition that may be caused or made worse by this is: https://bugs.launchpad.net/cinder/+bug/1357677 ** Affects: nova Importance: High Status: Confirmed ** Tags: libvirt volumes -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1359617 Title: libvirt: driver calls volume connect twice for every volume on boot Status in OpenStack Compute (Nova): Confirmed Bug description: Libvirt driver will attempt to connect the volume on the hipervisor twice for every volume provided to the instance when booting. If you examine the libvirt driver's spawn() method, both _get_guest_xml (by means of get_guest_storage_config) and _create_domain_and_network will call the _connect_volume method which works out the volume driver and then dispatches the connect logic. This is especially bad in the iscsi volume driver case, where we do 2 rootwraped calls in the best case, one of which is the target rescan, that can in theory add and remove devices in the kernel. I suspect that fixing this will make a number of races that have to do with the volume not being present when expected on the hypervisor, at least less likely to happen, in addition to making the boot process with volumes more performant. An example of a race condition that may be caused or made worse by this is: https://bugs.launchpad.net/cinder/+bug/1357677 To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1359617/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : yahoo-eng-team@lists.launchpad.net Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp
