I'm trying to setup live migration in Openstack
using Ceph RBD backed volumes. From what I understand I also
need to put the libvirt folder /var/lib/nova/instances on shared
storage for it to work as Nova tests for this as part of the
migration process. I decided to look at using CephFS for this
purpose.
I've created a CephFS file system and mounted it on my two
compute nodes as /var/lib/nova/instances but I'm getting some
strange results. It seems like after one of the hosts accesses a
file then it becomes locked and the other host can't access it.
For example, I complete the following steps:
1\ Create new Openstack instance using the boot from image
(create new volume) option. New instance is created with RBD
backed volume as expected. On the relevant compute host I see
the instance folder created under /var/lib/nova/instances/{
instance
id} with two files inside libvirt.xml and console.log. If
I cat the libvirt.xml file it works as expected.
2\ Live migrate the instance to other host. Appears to work as
expected although instance status in Horizon stays as migrating
forever. I can see instance has moved to second host by running
virsh list on both hosts.
4\ Now, if I attempt to cat the libvirt.xml file on the new host
I get "Operation not permitted".
I'm assuming this isn't what's expected?
To test this further I tried the following basic tests:
On Host 2:
root@devops-kvm02:/var/lib/nova/instances#
echo hello > test
root@devops-kvm02:/var/lib/nova/instances#
cat test
hello
root@devops-kvm02:/var/lib/nova/instances#
Then from Host 1:
root@devops-kvm01:/var/lib/nova/instances#
cat test
cat: test: Operation not permitted
root@devops-kvm01:/var/lib/nova/instances#
Then back on Host 2:
root@devops-kvm02:/var/lib/nova/instances#
cat test
cat: test: Operation not permitted
root@devops-kvm02:/var/lib/nova/instances#
Should this even work? My understanding is CephFS allows
concurrent access but I'm not sure if there is some file locking
going on that I need to understand.
Thanks,
Neville
