Gluster users - Nov 2016 - Automation of single server addition to replica

Replicas are defined in the order bricks are listed in the volume create 
command. So gluster volume create myvol replica 2 server1:/data/brick1 
server2:/data/brick1 server3:/data/brick1 server4:/data/brick1 will 
replicate between server1 and server2 and replicate between server3 and 
server4.

See also 
https://joejulian.name/blog/how-to-expand-glusterfs-replicated-clusters-by-one-server/

On 11/08/2016 03:28 PM, Lopez, Dan-Joe wrote:
>
> Hello All,
>
>                 I?d like to automate a gluster replica cluster in a 
> way that allows me to later add single servers on the fly.  I can?t 
> seem to understand from the docs how I might achieve this.  It seems 
> logical that a replica cluster needs to have at least 2 servers 
> initially, but thereafter, I see no reason that I shouldn?t be able to 
> add a single server to the cluster.  From what I have read, it seems 
> that the number of servers I add in the future needs to match the 
> number of servers that I started with.
>
> e.g. replica 1 doesn?t really make sense, and isn?t allowed, but if I 
> start with replica n; I must always add n servers at a time to the 
> volume, I can?t just add one server to have an n+1 replica?
>
> If anyone could point me in the right direction here, I?d really 
> appreciate it.
>
> Dan-Joe Lopez
>
>
>
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Il 09 nov 2016 1:23 AM, "Joe Julian" <joe at julianfamily.org>
ha scritto:
>
> Replicas are defined in the order bricks are listed in the volume create
command. So gluster volume create myvol replica 2 server1:/data/brick1
server2:/data/brick1 server3:/data/brick1 server4:/data/brick1 will
replicate between server1 and server2 and replicate between server3 and
server4.
>
> See also
https://joejulian.name/blog/how-to-expand-glusterfs-replicated-clusters-by-one-server/
>
i really hope this could be automated in newer gluster versions
There is almost no sense to make a replica on the same server so gluster
should automatically move bricks to preserve data consistency when adding
servers.

Ceph does this by moving objects around and you don't have to add servers
in a multiple of replica

the rebalance command could be used to rebalance newly added bricks by
preserving replicas in a proper state
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