[Linux-cluster] Using GFS without a network?

[Steve Wilcox]

On Tue, 2005-09-06 at 20:06 -0400, Steve Wilcox wrote:
> On Wed, 2005-09-07 at 00:57 +0200, Andreas Brosche wrote:
> 
> > > - Multi-initator SCSI buses do not work with GFS in any meaningful way,
> > > regardless of what the host controller is.
> > > Ex: Two machines with different SCSI IDs on their initiator connected to
> > > the same physical SCSI bus.
> > 
> > Hmm... don't laugh at me, but in fact that's what we're about to set up.
> > 
> > I've read in Red Hat's docs that it is "not supported" because of 
> > performance issues. Multi-initiator buses should comply to SCSI 
> > standards, and any SCSI-compliant disk should be able to communicate 
> > with the correct controller, if I've interpreted the specs correctly. Of 
> > course, you get arbitrary results when using non-compliant hardware... 
> > What are other issues with multi-initiator buses, other than performance 
> > loss?
> 
> I set up a small 2 node cluster this way a while back, just as a testbed
> for myself.  Much as I suspected, it was severely unstable because of
> the storage configuration, even occasionally causing both nodes to crash
> when one was rebooted due to SCSI bus resets.  I tore it down and
> rebuilt it several times, configuring it as a simple failover cluster
> with RHEL3 and RHEL4, a GFS cluster under RHEL4 and Fedora4, and as an
> openSSI cluster using Fedora3.  All tested configurations were equally
> crash-happy due to the bus resets.  
> 
> My configuration consisted of a couple of old Compaq deskpro PC's, each
> with a single ended Symbiosis card (set to different SCSI ID's
> obviously) and an external DEC BA360 jbod shelf with 6 drives.  The bus
> resets might be mitigated somewhat by using HVD SCSI and Y-cables with
> external terminators, but from my previous experience with other
> clusters that used this technique (DEC ASE and HP-ux service guard), bus
> resets will always be a thorn in your side without a separate,
> independent raid controller to act as a go-between.  Calling these
> configurations simply "not supported" is an understatement - this type
> of config is guaranteed trouble.  I'd never set up a cluster this way
> unless I'm the only one using it, and only then if I don't care one
> little bit about crashes and data corruption.  My two cents.
> 
> -steve


Small clarification - Although clusters from DEC, HP, and even
DigiComWho?Paq's TruCluster can be made to work (sort of) on multi-
initiator SCSI busses, IIRC it was never a supported option for any of
them (much like RedHat's offering).  I doubt any sane company would ever
support that type of config.

-steve