[Gluster-users] Is it possible to manually specify brick replication location?

[Joe Julian]

See if this helps with the concept you're working on: http://joejulian.name/blog/how-to-expand-glusterfs-replicated-clusters-by-one-server/

Michael Peek <peek at nimbios.org> wrote:

>Hi Gluster gurus,
>
>I'm new to Gluster, so if there is a solution already talked about
>somewhere then gladly point me to it and I'll get out of the way.  That
>said, here's my problem:
>
>I have four machines.  Each machine is running Ubuntu 12.04 with
>Gluster
>3.2.5.  Each machine has two drives:
>
>node1:/export/bricks/a
>node1:/export/bricks/b
>node2:/export/bricks/a
>node2:/export/bricks/b
>node3:/export/bricks/a
>node3:/export/bricks/b
>node4:/export/bricks/a
>node4:/export/bricks/b
>
>I created a volume with a single replication, added the bricks, mounted
>it to /mnt, and then created a file with "touch /mnt/this".  The file
>"this" appeared on the two bricks located on node1:
>
>node1:/export/bricks/a/this
>and
>node1:/export/bricks/b/this
>
>So if node1 goes down, all access to the file "this" is lost.  It
>seemed
>to me that the order in which bricks were added dictated the
>replication
>location -- i.e. the second brick added is used as the replication
>destination for the first brick, and so on with the 3rd and 4th pair of
>bricks, 5th and 6th, etc.
>
>I've searched the archives, and this seems to be confirmed in a past
>post located here:
>http://supercolony.gluster.org/pipermail/gluster-users/2013-June/036272.html
>
>> Replica sets are done in order that the bricks are added to the
>volume.
>...
>> So, you have an issue here, that both bricks of a replica set are on
>the 
>> same host.
>
>Unfortunately, this was the end of the thread and no more information
>was forthcoming.
>
>Now, I'm just starting out, and my volume is not yet used in
>production,
>so I have the luxury of removing all the bricks and then adding them
>back in an order that allows for replication to be done across nodes
>the
>way that I want.  But I see this as a serious problem.  What happens
>down the road when I need to expand?
>
>How would I add another machine as a node, and then add it's bricks,
>and
>still have replication done outside of that one machine?  Is there a
>way
>to manually specify master/replication location?  Is there a way to
>reshuffle replicant brick on a running system?
>
>A couple of solutions have presented themselves to me:
>1) Only add new nodes in pairs, and make sure to add bricks in the
>correct order.
>2) Only add new nodes in pairs, but setup two Gluster volumes and use
>geo-replication (even though the geographical distance between the two
>clusters may be as little as only 1 inch).
>3) Only add new nodes in pairs, and use RAID or LVM to glue the drives
>together, so that as far as Gluster is concerned, each node only has
>one
>brick.
>
>But each of these solutions involves adding new nodes in pairs, which
>increases the incremental cost of expansion more than it feels like it
>should.  It just seems to me that there should be a smarter way to
>handle things than what I'm seeing before me, so I'm hoping that I've
>just missed something obvious.
>
>So what is the common wisdom among seasoned Gluster admins?
>
>Thanks for your help,
>
>Michael
>
>
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>
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