OpenStack Compute (nova)

snapshots with lvm

Bug #1083714 reported by Adam Jacob Muller
10
This bug affects 1 person
Affects Status Importance Assigned to Milestone
OpenStack Compute (nova)
Invalid
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Bug Description

inside nova/virt/libvirt/driver.py/snapshot()

        xml_desc = virt_dom.XMLDesc(0)
        domain = etree.fromstring(xml_desc)
        source = domain.find('devices/disk/source')
        disk_path = source.get('file')

This is wrong because when LVM-backed disks are used:
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/dev/vg/instance-000003d1_disk'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>

It should therefore (with some tests obv) be:
disk_path = source.get('dev')

However, even if this is corrected:

# qemu-img snapshot -c foo /dev/vg/instance-000003d1_disk
qemu-img: Could not create snapshot 'foo': -95 (Operation not supported)

qemu-img doesn't seem to support snapshotting on lvm disks (and that doesn't necessarily seem like the right thing anyway)

Michael Still (mikal)
Changed in nova:
status: New → Triaged
importance: Undecided → Critical
Revision history for this message
Adam Jacob Muller (78luphr0rnk2nuqimstywepozxn9kl19tqh0tx66b5dki1xxsh5mkz9gl21a5rlwfnr8jn6ln0m3jxne2k9x1ohg85w3jabxlrqbgszpjpwcmvk-launchpad) wrote :

My, "this works but probably isn't even 100% right for LVM and DEFINITELY isn't right for non-lvm cases" patch:

--- a/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py
+++ b/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py
@@ -821,29 +821,7 @@ class LibvirtDriver(driver.ComputeDriver):
         xml_desc = virt_dom.XMLDesc(0)
         domain = etree.fromstring(xml_desc)
         source = domain.find('devices/disk/source')
- disk_path = source.get('dev')
-
- LOG.debug("creating snapshot")
- out, err = utils.execute('lvcreate',
- '-s',disk_path,
- '-L','10G',
- '-n',"_snap_%s"%snapshot_name,
- run_as_root=True)
- snap_file = '/dev/%s/_snap_%s' % (FLAGS.libvirt_images_volume_group,snapshot_name)
- LOG.debug("temporary_chown(%s) to %s" % (snap_file,os.getuid()))
- with utils.temporary_chown(snap_file):
- snap_h=open(snap_file,"r")
- LOG.debug("sending snapshot image to image service")
- image_service.update(context,
- image_href,
- metadata,
- snap_h)
- snap_h.close()
- out, err = utils.execute('lvremove',
- '-f',snap_file,
- run_as_root=True)
-
- return None
+ disk_path = source.get('file')

         (state, _max_mem, _mem, _cpus, _t) = virt_dom.info()
         state = LIBVIRT_POWER_STATE[state]

Revision history for this message
Thierry Carrez (ttx) wrote :

Support for snapshots on LVM and raw was added in grizzly-1:
https://blueprints.launchpad.net/nova/+spec/snapshots-for-everyone

It looks like your concerns have been adressed there, please reopen if you disagree.

Changed in nova:
importance: Critical → Undecided
status: Triaged → Invalid
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