On Fri, 9 Apr 2004, Bill Studenmund wrote:

> A simple example is a failover
> configuration, where the hot-spare computer can grab the disk on failure.

That is not quite so simple as it seems, actually, because for this to
work reliably (as opposed to trash the entire disk :-)) the takover host
needs to have some way to ensure that the allegedly failed host cannot,
even if it wants to, use that disk any more. Basically, the host taking
over the device needs some sort of "cutoff switch" under its control that
cuts off the other host from the system in question.

The issue is, of course, that the allegedly malfunctioning host may seem
to be down, but may not really be down (or down enough), and may still
try to use that device.

cjs
-- 
Curt Sampson  <cjs@cynic.net>   +81 90 7737 2974   http://www.NetBSD.org
    Don't you know, in this new Dark Age, we're all light.  --XTC