<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On 10 June 2015 at 22:38, Aravinda <span dir="ltr"><<a href="mailto:avishwan@redhat.com" target="_blank">avishwan@redhat.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div>On 06/10/2015 09:43 PM, Gabriel Kuri
wrote:<br>
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<div>> 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. <br>
> Other two volumes should be read-only till volume in
server-A fails for some reason.<br>
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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?<br>
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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.<br>
<br>
Replicated Volumes:<br>
--------------------------<br>
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. <br>
<br>
Replication is between bricks of single volume.<br>
<br>
Geo-replicated Volumes:<br>
--------------------------------<br>
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.<br>
<br>
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.<span class=""><br>
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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?<br>
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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.<br></div></blockquote><div><br></div><div>Yes, I think you are confused between replication and geo-replication.<br><br></div><div>Just to add to what Aravinda mentioned, in AFR (Automatic File Replication, that's what it's called in glusterfs) the replication happens between the bricks of the same volume. The bricks are expected to be part of same network. And the replication is synchronous. You can read more at <a href="http://gluster.readthedocs.org/en/latest/Features/afr-v1/index.html?highlight=afr">http://gluster.readthedocs.org/en/latest/Features/afr-v1/index.html?highlight=afr</a><br><br></div><div>And glusterfs geo-replication is between two (or more) glusterfs volumes. These volumes in turn can have replicated setup internally. And volumes are generally in different networks. And it's asynchronous one way replication. It's mainly used for disaster recovery. <br><br></div><div>I found below link which is very old. But the content seems to be valid still<br><br><b><a href="http://www.gluster.org/community/documentation/index.php/Gluster_3.2:_Replicated_Volumes_vs_Geo-replication">http://www.gluster.org/community/documentation/index.php/Gluster_3.2:_Replicated_Volumes_vs_Geo-replication</a></b><br><br></div><div>HTH<br></div><div><br></div><div>Greetings,<br></div><div>Vishwanath<br><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
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>> If it's not master-master, how does one get
master-master replication working over a WAN?<br>
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<div>> AFAIK, there is no work around as of now, at least I
am not aware of it<br>
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<div>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?<br>
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<div>Thanks ...<br>
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<pre cols="72">--
regards
Aravinda</pre>
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