Snapmirror - Intercluster link selection logic

[steven_langdale]

Hi All

Does anyone know what logic is used by the snapmirror process to work out what intercluster links are used for a snapmirror process?

Does it uses the ones on the node that's the owner of the aggr containing source / target volume? 

[TMACMD]

When you setup cluster peering, you *must* setup a full mesh. Each node on both sides must have an InterCluster LIF. Each and every LIF MUST be able to ping EACH and EVERY LIF. 

If you put yourself in a scenario where you have multiple mirrors:

Clus1 -> Clus2

Clus1 -> Clus3

BUT Clus2 CANNOT see or reach Clus3 then you need to make a modification!

In this case, on Clus1, you must create an IPSPACE for one of the two mirrors. Why? If I setup all IP on Clus1, Clus2 can only get to half of them and cluster peering will fail eventually. Same with Clus3 (it can only get to half the IPs).

By creating the IPspace on Clus1 for the Clus1-Clus3 relationship, Clus2 will only ever know about the IPs it communicates with and Clus3 will only know about the IPs it needs to communicate with. You basically isolate the traffic, kinda like a VLAN in so much as it prevents cross-talk between the IPspaces.

[steven_langdale]

Hi

Yep thats understood, but that's not what I'm after.

Lets say I have a 2 node cluster peered with a 2nd 2 node cluster.  We have a total of 4 intercluster interfaces.

I have 3 snapmirrors from cluster A to cluster B.  Which intercluster links does it use?  whats the logic for picking the source and destination for each snapmirror process?

Makes sense?

[TMACMD · Accepted solution]

Forgot to include that

 the logic is simple. By setting up the full mesh every node can talk to every node. The mirror finds the two nodes involved as a source and a destination and uses those. If the source or destination volume moves so will the LIF being used to compensate for the volume move

 make sense?

 If that works please mark as solved. 
thanks

[steven_langdale]

Hi 

In that a volume isn't bound to a node, but the underlying aggregate is.  I assume the LIF used is the one bound to the node that own's the aggregate that contains the volume?  

[TMACMD]

Exactly.