Re: Expanding Volumes and Geo-replication

[M S Vishwanath Bhat <vbhat@xxxxxxxxxx>]

On 04/09/14 00:33, Vijaykumar Koppad wrote:

On Wed, Sep 3, 2014 at 8:20 PM, M S Vishwanath Bhat <vbhat@xxxxxxxxxx> wrote:

On 01/09/14 23:09, Paul Mc Auley wrote:

Hi Folks,

Bit of a query on the process for setting this up and the best practices for same.

I'm currently working with a prototype using 3.5.2 on vagrant and I'm running into assorted failure modes with each pass.

The general idea is I start with two sites A and B where A has 3 bricks used to build a volume vol at replica 3 and
B has 2 bricks with at replica 2 to also build vol.
I create 30 files is A::vol and then set up geo-replication from A to B after which I verify that the files have appeared in B::vol.
What I want to do then is double the size of volumes (presumably growing one and not the other is a bad thing)
by adding 3 bricks to A and 2 bricks to B.

I've had this fail number of ways and so I have a number of questions.

Is geo-replication from a replica 3 volume to a replica 2 volume possible?

Yes. geo-replication just needs two gluster volumes (master -> slave). It doesn't matter what configuration master and slave has. But slave should be big enough to have all the data in master.

Should I stop geo-replication before adding additional bricks? (I assume yes)

There is no need to stop geo-rep while adding more bricks to the volume.

Should I stop the volume(s) before adding additional bricks? (Doesn't _seem_ to be the case)

No.

Should I rebalance the volume(s) after adding the bricks?

Yes. After add-brick, rebalance should be run.

Should I need to recreate the geo-replication to push-pem subsequently, or can I do that out-of-band?
...and if so should I have to add the passwordless SSH key back in? (As opposed to the restricted secret.pem)
For that matter in the inital setup is it an expected failure mode that the initial geo-replication create will fail if the slave host's SSH key isn't known?

After the add-brick, the newly added node will not have any pem files. So you need to do "geo-rep create push-pem force". This will actually push the pem files to the newly added node as well. And then you need to do "geo-rep start force" to start the gsync processes in newly added node.

So the sequence of steps for you will be,

1. Add new nodes to both master and slave using gluster add-brick command.

After this, we need to run  "gluster system:: execute gsec_create " on master node and then proceed with step 2.

Yeah. Missed it... Sorry :)

The pem files needs to be generated for the newly added nodes before pushing them to slave. Above command does that.

2. Run geo-rep create push-pem force and start force.
3. Run rebalance.

Hope this works and hope it helps :)


Best Regards,
Vishwanath

Thanks,
    Paul
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