On 06/10/2015 09:43 PM, Gabriel Kuri wrote:
> 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.
So the writes from the client will go directly to whichever server is
the master, even though the client has mounted the volume on one of
the slaves? What about the reads, do they still hit the server (ie
slave) the client is connected to or do the reads hit the master as well?
To be specific, Gluster Geo-rep doesn't support Master-Master. That
means no automatic failover when master Volume goes down. Gluster
replicated volumes support Master-Master within the Volume.
Replicated Volumes:
--------------------------
The replication is synchronous, all writes on the mount will be copied
to multiple bricks(replica count) synchronously. If one node is down
during the write, other nodes takes care of syncing data when node comes
online. This is automatic using self-heal.
Replication is between bricks of single volume.
Geo-replicated Volumes:
--------------------------------
Asynchronous replication of whole Gluster Volume. That means their will
be delay in syncing data from Master Volume to Slave Volume. Volume
topology does not matter Geo-replication works even if Master and Slave
Volume types are different.
Geo-replication is mainly used as disaster recovery mecanism like
backups. Manual failover failback is also supported, if Master Volume
goes down Slave Volume can become Master and can establish connection
back. It is not supported to have Georep running in both ways at same time.
In the case of geo-rep, how is split-brain handled? If the network is
down between server A (master) and server B (slave) and the client has
mounted to server B, I assume server B will then become the master and
writes will then be committed directly to server B, but if writes were
also committed to server A by other clients while the network was
down, what happens when the network is back up between server A and B,
does it just figure out which files had the most recent time stamp and
commit those changes across all the servers?
Since Master-Master is not supported in Geo-rep, Split brain is not
handled. I think there is some confusion between replicated volume and
geo-rep. Replicated Volume replicates data within Volume. For example,
Create a Gluster Volume with two bricks with replica count as 2.
Bricks/Nodes cannot be across data centers. In case of Geo-rep,
replication is between two Gluster Volumes.
>> 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
Does the basic replicated volume work in this fashion, reads and
writes to all servers? The only problem is it's meant for a low
latency network environment?
Thanks ...
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--
regards
Aravinda
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