[Linux-cluster] 2-node fencing question

[Riaan van Niekerk]

> However, it could very well be that IPMI hardware modules are slow
> enough at processing requests that this could pose a problem.  What
> hardware has this happened on?  Was ACPI disabled on boot in the host OS
> (it should be; see below)?
> 
> 
snip
> 
> The time window for (c) increases significantly (5+ seconds) if the
> cluster nodes are enabling ACPI power events on boot.  This is one of
> the reasons why booting with acpi=off is required when using IPMI, iLO,
> or other integrated power management solutions.
> 
> If booting with acpi=off, does the problem persist?
> 

Lon - is the requirement for disabling acpi when using integrated fence 
devices documented anywhere?

I have searched far and wide on the nature of acpi=off (if it is good or 
bad, recommended by Red Hat or anyone out there). Yours is the strongest 
against acpi enabled I have found, but not for reasons I would have 
expected.

My impression of acpi=off is it borders on a magical cure-all for 
boot/installation problems (in part due to bad acpi by server/firmware 
vendors), but that it also acts as some kind of safe mode (e.g. ht is 
disabled, does things to IRQ routing, etc) which may have an adverse 
effect on system performance.

Are you aware of any negative effects, performance or otherwise, which 
acpi=off will cause. E.g. if the only adverse effect of acpi=off is 
hyperthreading being disabled, users that want it back, can so using acpi=ht

Riaan

note: IMHO, a Knowledge Base article on the use of acpi=off (and its 
variants), for general RHEL installations, and pertaining to RHCS/GFS 
implementations would be very welcome.
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