Public bug reported:
Description
===========
If an instance has had an attached volume volume-updated twice in a
"round-trip" - ie, volume-update $vol1 $vol2, then volume-update $vol2
$vol1 - it cannot be live-migrated.
Steps to reproduce
==================
1. Create two iscsi volumes.
# cinder create --name test_vol1 --volume-type iscsi 1
# cinder create --name test_vol2 --volume-type iscsi 1
(--volume-type iscsi isn't mandatory - in my devstack environment there is
no iscsi
volume-type, but that doesn't stop me from reproducing this bug)
2. Boot an instance.
# nova boot --flavor 1 --image $imageid --nic net-id=$netid testvm1
3. Attach one iscsi volume to testvm1.
# nova volume-attach testvm1 $test_vol1
4. Do volume-update to swap volume to 2nd one. (1st time volume-update)
# nova volume-update testvm1 $test_vol1 $test_vol2
5. Do volume-update again to swap volume back to the 1st one. (2nd time
volume-update)
# nova volume-update testvm1 $test_vol2 $test_vol1
6. Live migrate instance to other compute node.
# nova live-migration testvm1
Expected result
===============
Live migration succeeds.
Actual result
=============
Live migration fails with:
Apr 27 10:32:14 multi9h-3 nova-compute: File "/usr/lib64/python2.7/site-
packages/libvirt.py", line 1939, in migrateToURI3
Apr 27 10:32:14 multi9h-3 nova-compute: if ret == -1: raise libvirtError
('virDomainMigrateToURI3() failed', dom=self)
Apr 27 10:32:14 multi9h-3 nova-compute: libvirtError: missing source
information for device vdb
Environment
===========
This has been originally reported [1] in Red Hat OSP 9 (Mitaka) and is
reproducible on devstack master as well.
Additional information
======================
There are two things going on here.
1. When performing the volume-update, the libvirt driver calls
virDomainBlockRebase without the VIR_DOMAIN_BLOCK_REBASE_COPY_DEV flag
[2], meaning the device XML changes from <source dev=/dev/isci/lun> to
<source file=/dev/iscsi/lun>. This is a problem because /dev/iscsi/lun
isn't a regular file, and causes the above error, except you need the
"round-trip" volume-update to trigger it. Why? Because:
2. The serial number isn't updated when doing volume-update, and there's
a bit of live-migration code [3] that checks for serial numbers before
updating the XML. If the serial numbers don't match, the XML isn't
updated, and libvirt doesn't notice that /dev/iscsi/lun isn't a file.
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1446446
[2] http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainBlockRebase
[3]
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/migration.py#L158
** Affects: nova
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1691195
Title:
Can't live-migrate after "round-trip" volume-upate
Status in OpenStack Compute (nova):
New
Bug description:
Description
===========
If an instance has had an attached volume volume-updated twice in a
"round-trip" - ie, volume-update $vol1 $vol2, then volume-update $vol2
$vol1 - it cannot be live-migrated.
Steps to reproduce
==================
1. Create two iscsi volumes.
# cinder create --name test_vol1 --volume-type iscsi 1
# cinder create --name test_vol2 --volume-type iscsi 1
(--volume-type iscsi isn't mandatory - in my devstack environment there is
no iscsi
volume-type, but that doesn't stop me from reproducing this bug)
2. Boot an instance.
# nova boot --flavor 1 --image $imageid --nic net-id=$netid testvm1
3. Attach one iscsi volume to testvm1.
# nova volume-attach testvm1 $test_vol1
4. Do volume-update to swap volume to 2nd one. (1st time volume-update)
# nova volume-update testvm1 $test_vol1 $test_vol2
5. Do volume-update again to swap volume back to the 1st one. (2nd time
volume-update)
# nova volume-update testvm1 $test_vol2 $test_vol1
6. Live migrate instance to other compute node.
# nova live-migration testvm1
Expected result
===============
Live migration succeeds.
Actual result
=============
Live migration fails with:
Apr 27 10:32:14 multi9h-3 nova-compute: File "/usr/lib64/python2.7
/site-packages/libvirt.py", line 1939, in migrateToURI3
Apr 27 10:32:14 multi9h-3 nova-compute: if ret == -1: raise
libvirtError ('virDomainMigrateToURI3() failed', dom=self)
Apr 27 10:32:14 multi9h-3 nova-compute: libvirtError: missing source
information for device vdb
Environment
===========
This has been originally reported [1] in Red Hat OSP 9 (Mitaka) and is
reproducible on devstack master as well.
Additional information
======================
There are two things going on here.
1. When performing the volume-update, the libvirt driver calls
virDomainBlockRebase without the VIR_DOMAIN_BLOCK_REBASE_COPY_DEV flag
[2], meaning the device XML changes from <source dev=/dev/isci/lun> to
<source file=/dev/iscsi/lun>. This is a problem because /dev/iscsi/lun
isn't a regular file, and causes the above error, except you need the
"round-trip" volume-update to trigger it. Why? Because:
2. The serial number isn't updated when doing volume-update, and
there's a bit of live-migration code [3] that checks for serial
numbers before updating the XML. If the serial numbers don't match,
the XML isn't updated, and libvirt doesn't notice that /dev/iscsi/lun
isn't a file.
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1446446
[2] http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainBlockRebase
[3]
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/migration.py#L158
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