[c-nsp] Catalyst 6500 Supervisor Engine Redundancy

[Sam Stickland]

Lasher, Donn wrote:
> I would only offer one caveat as to Redundancy mode discussions.
>
> For software-related failures, SSO may actually hurt you more than it
> helps.
>
> SSO, at least in my experience in the past (was SRM as I recall), is a
> complete "mirror" of one proc to the other. This means any memory
> corruption issues, stack problems, IOS issues, that may cause the first
> Proc to crash, may then crash the other proc as well, leading to a
> chassis reboot. Badness.
>
> RPR+, while taking longer to fail over compared to SSO, avoids those
> issues, by being "warm" but not "hot" standby.
>
> For hardware related failures on the other hand, SSO > RPR*
>   
Can anyone else offer any thoughts on this subject? From our prespective 
we hardly ever see any supervisors fail (linecards are of course a 
different story), but quite a lot of software related crashes, so it 
sounds like SSO isn't a great solution from _our_ prespective (YMMV).

The described "double failure" mechanism above certainly sounds 
plausible - has anyone got any real-world experience of it?

S