[openstack-dev] instance migration strangeness in devstack

Dan Genin daniel.genin at jhuapl.edu
Thu Jan 16 16:04:06 UTC 2014

Thank you for replying, Vish. I did sync and verified that the file was 
written to the host disk by mounting the LVM volume on the host.

When I tried live migration I got a Horizon blurb "Error: Failed to live 
migrate instance to host" but there were no errors in syslog.

I have been able to successfully migrate a Qcow2 backed instance.

On 01/16/2014 03:18 AM, Vishvananda Ishaya wrote:
> This is probably more of a usage question, but I will go ahead and 
> answer it.
> If you are writing to the root drive you may need to run the sync 
> command a few times to make sure that the data has been flushed to 
> disk before you kick off the migration.
> The confirm resize step should be deleting the old data, but there may 
> be a bug in the lvm backend if this isn’t happening. Live(block) 
> migration will probably be a bit more intuitive.
> Vish
> On Jan 15, 2014, at 2:40 PM, Dan Genin <daniel.genin at jhuapl.edu 
> <mailto:daniel.genin at jhuapl.edu>> wrote:
>> I think this qualifies as a development question but please let me 
>> know if I am wrong.
>> I have been trying to test instance migration in devstack by setting 
>> up a multi-node devstack following directions at 
>> http://devstack.org/guides/multinode-lab.html. I tested that indeed 
>> there were multiple availability zones and that it was possible to 
>> create instances in each. The I tried migrating an instance from one 
>> compute node to another using the Horizon interface (I could not find 
>> a way to /confirm///migration, which is a necessary step, from the 
>> command line). I created a test file on the instance's ephemeral 
>> disk, before migrating it, to verify that the data was moved to the 
>> destination compute node. After migration, I observed an instance 
>> with the same id active on the destination node but the test file was 
>> not present.
>> Perhaps I misunderstand how migration is supposed to work but I 
>> expected that the data on the ephemeral disk would be migrated with 
>> the instance. I suppose it could take some time for the ephemeral 
>> disk to be copied but then I would not expect the instance to become 
>> active on the destination node before the copy operation was complete.
>> I also noticed that the ephemeral disk on the source compute node was 
>> not removed after the instance was migrated, although, the instance 
>> directory was. Nor was the disk removed after the instance was 
>> destroyed. I was using LVM backend for my tests.
>> I can provide more information about my setup but I just wanted to 
>> check whether I was doing (or expecting) something obviously stupid.
>> Thank you,
>> Dan
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