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Hi Gluster gurus,<br>
<br>
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:<br>
<br>
I have four machines. Each machine is running Ubuntu 12.04 with
Gluster 3.2.5. Each machine has two drives:<br>
<br>
node1:/export/bricks/a<br>
node1:/export/bricks/b<br>
node2:/export/bricks/a<br>
node2:/export/bricks/b<br>
node3:/export/bricks/a<br>
node3:/export/bricks/b<br>
node4:/export/bricks/a<br>
node4:/export/bricks/b<br>
<br>
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:<br>
<br>
node1:/export/bricks/a/this<br>
and <br>
node1:/export/bricks/b/this<br>
<br>
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.<br>
<br>
I've searched the archives, and this seems to be confirmed in a past
post located here:<br>
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<a
href="http://supercolony.gluster.org/pipermail/gluster-users/2013-June/036272.html">http://supercolony.gluster.org/pipermail/gluster-users/2013-June/036272.html</a><br>
<br>
<blockquote type="cite">
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<pre style="white-space: pre-wrap; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Replica sets are done in order that the bricks are added to the volume.</pre>
</blockquote>
...<br>
<blockquote type="cite">
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charset=ISO-8859-1">
<pre style="white-space: pre-wrap; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">So, you have an issue here, that both bricks of a replica set are on the
same host.</pre>
</blockquote>
<br>
Unfortunately, this was the end of the thread and no more
information was forthcoming.<br>
<br>
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?<br>
<br>
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?<br>
<br>
A couple of solutions have presented themselves to me:<br>
1) Only add new nodes in pairs, and make sure to add bricks in the
correct order.<br>
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).<br>
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.<br>
<br>
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.<br>
<br>
So what is the common wisdom among seasoned Gluster admins?<br>
<br>
Thanks for your help,<br>
<br>
Michael<br>
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