Re: Linux Cluster using shared scsi

[Pavel Machek <pavel@suse.cz>]

Hi!

> > > ...
> > >
> > > If told to hold a reservation, then resend your reservation request once every
> > > 2 seconds (this actually has very minimal CPU/BUS usage and isn't as big a
> > > deal as requesting a reservation every 2 seconds might sound).  The first time
> > > the reservation is refused, consider the reservation stolen by another machine
> > > and exit (or optionally, reboot).
> > 
> > Umm. Reboot? What do you think this is? Windoze?
> 
> It's the *only* way to guarantee that the drive is never touched by more than
> one machine at a time (notice, I've not been talking about a shared use drive,
> only one machine in the cluster "owns" the drive at a time, and it isn't for
> single transactions that it owns the drive, it owns the drive for as long as
> it is alive, this is a limitation of the filesystes currently available in
> mainstream kernels).  The reservation conflict and subsequent reboot also
> *only* happens when a reservation has been forcefully stolen from a
>machine. 

I do not believe reboot from kernel is right approach. Tell init with
special signal, maybe; but do not reboot forcefully. This is policy;
doing reboot might be right answer in 90% cases; that does not mean
you should do it always.

How is "reservation error" different from any other error? What if
drive generates reservation error by mistake?

I believe drive should be considered dead until reboot after
"reservation error". That way you do not damage data by default, and
provide user option with doing whatever is appropriate.
								Pavel
-- 
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org