Number of network adaptors needed in RAC

Question

hello guys,
in oracle RAC each node must have a minimum of 3 adaptors. one for private interconnect, one for public interconnect and one for serving the user requests (VIP).
1. also in oracle 11g with the introduction of SCAN. do we have to add a new network adaptor to make use of scan or can the network adaptor using the VIP address can be used for SCAN. if SCAN requires a new adaptor then it makes 4 n/w adaptors needed for each node,
2. Oracle documentation says that SCAN can be resolved to at most 3 network addresses. what happens if we have a RAC with more than 3 nodes.
3. How does this SCAN really work. it says that scan be used as a single IP address instead of defining several ip address in the tnsnames.ora file at the client side.
4. moreover the these SCAN ip Addresses are assigned by the DNS. i dont understand how can more than 2 system share a same ip address.
can any one help me understand these concepts please...

Answer 1

vishnusivathej wrote:
hello guys,
in oracle RAC each node must have a minimum of 3 adaptors. one for private interconnect, one for public interconnect and one for serving the user requests (VIP).I believe its not correct. There should be two adaptors only. One for the private interconnect, one for the pulbic. The VIP is going to be using the public interconnect only. The third one, is going to be required if you are going to be using it for storage.
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1. also in oracle 11g with the introduction of SCAN. do we have to add a new network adaptor to make use of scan or can the network adaptor using the VIP address can be used for SCAN. if SCAN requires a new adaptor then it makes 4 n/w adaptors needed for each node,SCAN IP would be separate from the VIP. I am not sure that you need a separate adaptor for it since its also going to be a public IP.
2. Oracle documentation says that SCAN can be resolved to at most 3 network addresses. what happens if we have a RAC with more than 3 nodes.There is no mandatory thing that you need 3 SCAN network addresses. One can be used as well. 3 is the suggested setting for the setup. I believe for nodes more than 3 too, this would work. I have not installed 11.2 RAC for more than 3 nodes yet so can't be sure .
3. How does this SCAN really work. it says that scan be used as a single IP address instead of defining several ip address in the tnsnames.ora file at the client side.That's wrong. There is nothing like single IP address.SCAN is Single Cluster Access Name which means instead of putting VIPs in the client side tnsnames.ora, you are going to put just a SCAN cluster name whose VIP address resolutio is going to be done with the help of your DNS . Please read the documentation which explains the concept in lot more detail.
4. moreover the these SCAN ip Addresses are assigned by the DNS. i dont understand how can more than 2 system share a same ip address.Not sure that I got your statement.
HTH
Aman....