[LinuxFailSafe] SCSI Hardware

[Alan Robertson]

Joshua Rodman wrote:
> 
<snip>
> With this in mind, a shareable SCSI bus certainly can be made highly
> available, and scripts to control the failover of a shared-storage
> filesystem shouldn't be too difficult to write (I would expect them to get
> written/published soon enough).

Actually, that's not quite true.  A true shared SCSI bus is a single point of
failure.  If you get a stuck-at fault on any lead on the bus, it mostly won't
work for either machine.  In other words, a fried disk controller can easily
hang the whole bus.  You really need a fully isolated bus for each machine which
can access the RAID controller.  The RAID controller itself needs to be
internally redundant and provide isolated interfaces to each machine.  This
costs between $5K and $15K.

> The tricky bit, which is what you're really asking, is 'Can I set up
> Linux to share a SCSI bus with multiple intiators?' which is really more
> of a Linux kernel/driver question than a Failsafe question.  Of course it
> is very relevant to Failsafe, so pointers on the topic would be great..
> but I don't know the current status of these issues myself, sorry.

I think the Kimberlite folks have lots of information on this score.

	-- Alan Robertson
	   alanr@suse.com