Question about replica set node failures

[ejholm]

I have a quick question regarding a failure in the replica set. We have a 4 node system with an arbiter. 2 nodes are in our primary data center and 2 nodes are in our DR data center. The arbiter is configured in our DR data center on a seperate server. I know that the arbiter should be in a 3rd data center, but at this time the powers that be want it to remain in the DR data center. So the architecture is laid out. Our primary node is in our primary data center along with a secondary. In the event that we lose the whole DR data center, can we still write to our primary node even though a majority of the voting nodes are missing? If you could respond and explain that would be very helpful.

 

My understanding is that once you lose a majority of the voting nodes that writes can no longer occur on the replica set.

 

Thanks,

 

Erik

[Stephen Steneker]

I have a quick question regarding a failure in the replica set. We have a 4 node system with an arbiter. 2 nodes are in our primary data center and 2 nodes are in our DR data center. The arbiter is configured in our DR data center on a seperate server. I know that the arbiter should be in a 3rd data center, but at this time the powers that be want it to remain in the DR data center. So the architecture is laid out. Our primary node is in our primary data center along with a secondary. In the event that we lose the whole DR data center, can we still write to our primary node even though a majority of the voting nodes are missing? If you could respond and explain that would be very helpful.

 

My understanding is that once you lose a majority of the voting nodes that writes can no longer occur on the replica set.

Hi Erik,

Your understanding is correct.  If your arbiter is in the DR and you lost connectivity to the main DC, you will end up with:

 - 2 nodes in the main DC (read only)

 - a new primary elected in the DR data center, because it still has a majority of nodes (3/5)

Cheers,

Stephen