ONTAP Hardware

Modules of the stack on the same PCI card


Config Advisor report, showed some Low Impact - Modules of the stack on the same PCI card.


We have two SAS stacks and one Quad SAS Port in each controller. After mapping out the cabling,  basically Ports 1a(first shelf)/1c(last shelf) are going to one stack and Ports 1d(first shelf)/1b(last shelf) are going to second stack.


I know the SAS cabling guide tells you to pair up ports so that  1a/1d does one stack and 1b/1c does the other stack, and I know ports A and B share the same ASIC as do C and D.


What impact is there by using 1a and 1c for one stack and 1b and 1d on another stack?


The obvious impact is, if your SAS controller fails, you lose access to disks. Using two independ controllers to connect disks improves resiliency.


I understand that having one HBA is a single point of failure but the cabling guide shows an example of using just one Quad SAS port HBA. Why does the guide not say you will get warnings if you use one HBA?


My point is by using just one HBA, the guide says the A must start one stack and C must start the other stack. Putting aside that we have one HBA, what is the impact of having A starting one stack and D starting the other stack?


So the guide shows all the supported configs, even if they are not best practices. Because it is not best practice you get the warning in Config Advisor.


But even if your setup is not best practice, it stil can make sense for your specific needs. With having an warning in Config Advisor you are aware of this risk and you can decide if you can live with this risk or if you have to change your setup to address this risk.