On IOM6s that have been upgraded to supported firmware and configured to use in-band, as well as IOM12s. How does the SAS channel actually issue the reset to the SAS chip / IOM that has stopped responding?
I see in this doc https://kb.netapp.com/app/answers/answer_view/a_id/1029778 it states: "The Alternate Control Path (ACP) interface currently uses Ethernet-based network connectivity to perform various recovery tasks, such as expander resets and shelf power cycles. This feature was referred to as Out-of-Band (OOB) ACP. With ONTAP 9.0 and later, ACP uses available SAS data links to perform the same tasks. This feature is referred to as In-Band ACP. The ACP mode that is configured applies to the entire ONTAP cluster."
But with the SAS cable plugged in to the SAS chip, and the SAS chip is offline.. how does it reboot it should it lock?
As much as i know there's very few scenarios any automatic recovery via ACP will be attempted (exemple for a bad one in BUG 868319). i don't believe it include issuing a full shelf powercycle. but it is available by command (and so as other reset and power_cycle commands) if you wish to issue them manually.