RAC Diagram: Where does HBA card fit in?

Question

Version : 11g
I know that all nodes in a RAC configuration have an HBA card and that HBA is somehow connected to the Shared storage. In the following link, we can see that, through NIC meant for public IP, nodes connect to Shared storage.
http://www.akadia.com/services/ora_rac.html
So, where does HBA fit in the whole RAC set up?

Answer 1

GarryB wrote:
So, where does HBA fit in the whole RAC set up?At physical h/w and driver level.
For the public RAC network you use what? A network card (aka NIC) and a network driver.
An HBA is like a NIC. But instead of wiring into a network switch, it wires via fibre into a storage array switch (where the switch connects to a SAN). It also needs a driver.
Typically HBAs have dual fibre channel ports. This means that the kernel, via the driver, will see the very same storage device (aka LUN), twice. Once via the one port and then again via the second port.
A LUN will however have a unique identifier (called a <i>WWID</i>). A driver (typically Multipath on Linux, or Powerpath when using EMC) is used to create a logical device that Oracle CRS and ASM can use. It uses the WWIDs to determine the unique device (LUN) and then creates a single logical devices that "sits on top" of the physical devices that points to the very same LUN on the storage server.
So instead of the application layer having to deal with the complexities of mulltiple I/O paths to a LUN, this is done by the driver. The application layer simply uses the logical multipath device and the multipath driver does the rest.
So a HBA is pretty low down in RAC architecture - and RAC itself does not deal directly with it. Just like it does not deal directly with a NIC and its settings.
PS. As already mentioned, the URL you referred to uses IP as a storage protocol and thus a NIC instead of a HBA. Questionable whether this is a good idea as a HBA provides dual 2Gb pipes - and the typical NIC used will be shared IP running at best at 1Gb, using a high latency protocol like TCP. A better option than HBAs are using HCAs and Infiniband instead. This runs dual ports at 40Gb (each) using the low latency SRP storage protocol.