[Gluster-users] geo-replication vs replicated volumes

[M S Vishwanath Bhat]

On 10 June 2015 at 12:24, Gabriel Kuri <gkuri at ieee.org> wrote:

> I need some clarification on how geo-replication (gluster => 3.5)
> operates, as I'm not fully understanding how the new and improved version
> works from the docs.
>
> Let's assume the following scenario, three servers setup in a geo-rep
> cluster all separated by a WAN:
>
> <server a> -- WAN -- <server b> -- WAN -- <server c>
>
> Does this scenario allow for a client with the a volume mounted to write
> to any of the servers directly and the write then gets replicated from that
> server to the other servers? For example, a client has the volume mounted
> (via FUSE) on server C and writes a file, does that file get written to
> server C directly and then the file replicates (asynchronously) to server A
> and server B ? Or is it that the writes only occur on the "master" of that
> geo-rep volume? I'm trying to understand if the replication for geo-rep
> occurs in a master-master setup or if it's still master-slave ? What was
> the big change for geo-rep in 3.5 ?
>

glusterfs doesn't support master-master yet. In your case, one of the
servers (A or B or C) should be a master and your client should write to
only that volume. Other two volumes should be read-only till volume in
server-A fails for some reason.

The big change in glusterfs-3.5 was the design of the geo-replication.
Earlier one single node in master volume was responsible for syncing data
to slave (which has lots of performance problems). So from > glusterfs-3.5,
the responsibility of syncing is shared across servers of volume in master.

>
> If it's not master-master, how does one get master-master replication
> working over a WAN?
>

AFAIK, there is no work around as of now, at least I am not aware of it

Best Regards,
Vishwanath


> Thanks ...
>
>
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