[Gluster-users] Question about redundancy

[Ron Kelley]

Greetings all,

I have a question about scalability and redundancy and am looking for some pointers/advice.

Suppose I have setup a 4-node distributed-replicated gluster configuration that was created using the command, 
"gluster volume create test-volume replica 2 transport tcp server1:/brick1 server2:/brick1 server3:/brick1  server4:/brick1"

From what I understand after reading the gluster docs and doing my own lab tests, it seems all the data contained on the replica pair will be lost of both servers in the replica fail.  For example, if I loose nodes 3 and 4 at the same time, all the data contained on those nodes is lost.  How can I get gluster to identify a node outage and replicate the data from server3 to servers1&2 if server 4 fails?  Is there some sort of command I can run so the data on node 4 gets replicated to node 1 or 2?

I have read some threads about creating a 3-node replica, but that only gives me 33% of the disk space since we are replicating the data to two other nodes.  In addition, if I need more space, I have to add 3 more nodes to the pool since the replica count is 3.  Seems like a big waste of money.

My goal is to build a storage infrastructure using Gluster to hold virtual machine images and other data for our infrastructure that can survive multiple node failures.  These servers are high-quality SuperMicro servers with LSI RAID controllers, plenty of RAM and CPU.  However, in the very unlikely event we loose 2 servers, I don’t want to loose any data.  


Thanks,

-Ron