RAC Interconnect Transfer rate vs NIC's Bandwidth

Question

Hi Guru,
I need some clarification for RAC interconnect terminology between "private interconnect transfer rate" and "NIC bandwidth".
We have 11gR2 RAC with multiple databases.
So we need to find out what the current resource status is.
We have two physical NICs each node. And 8G is for public and 2G is for private (interconnect).
Technically, we have 4G for Private network bandwidth.
If I look at the "Private Interconnect Transfer rate" though OEM or IPTraf (linux tool), it is showing 20 ~30 MB/Sec.
There is no any issue at all at this moment.
Please correct me if I am wrong.
The transfer rate will be fine till 500M or 1G/Sec. Because the current NIC's capacity is 4G. Does it make sense ?
I'm sure there are multiple things to consider,but I'm kind of stumped on the whole transfer rate vs bandwidth. Is there any way to calculate what a typical transfer would be....
OR How do I say our interconnect are good enough ....based on the transfer rate ?
Another question is ....
In our case, how do I set up the warning threshold and Critical threshold for "Private Interconnect Transer rate" in OEM ?
Any comments will be appreciated.
Please advise.

Answer 1

Interconnect performance sways more to latency than bandwidth IMO. In simplistic terms, memory is shared across the Interconnect. What is important for accessing memory? The size of the pipe? Or the speed of the pipe?
A very fast small pipe will typically perform significantly better than a large and slower pipe.
Even the size of the pipe is not that straight forward. Standard IP MTU size is 1500. You can run jumbo and super-jumbo frame MTU sizes on the Interconnect - where for example a MTU size of 65K is significantly larger than a 1500 byte MTU. Which means significantly more data can be transferred over the Interconnect at a much reduced overhead.
Personally, I would not consider Ethernet (GigE included) for the Interconnect. Infiniband is faster, more scalable, and offers an actual growth path to 128Gb/s and higher.
Oracle also uses Infiniband (QDR/40Gb) for their Exadata Database Machine product's Interconnect. Infiniband also enables one to run Oracle Interconnect over RDS instead of UDP. I've seen Oracle reports to the OFED committee saying that using RDS in comparison with UDP, reduced CPU utilisation by 50% and decreased latency by 50%.
I also do not see the logic of having a faster public network and a slower Interconnect.
IMO there are 2 very fundamental components in RAC that determines what is the speed and performance achievable with that RAC - the speed, performance and scalability of the I/O fabric layer and for the Interconnect layer.
And Exadata btw uses Infiniband for both these critical layers. Not fibre. Not GigE.