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Re: [Linux-cluster] Using GFS without a network?



On Wed, 2005-09-07 at 19:43 +1000, Keith Hopkins wrote:
> Steve Wilcox wrote:
> > 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   
> > 
> 
> HP-UX ServiceGuard words well with multi-initiator SCSI configurations, and is fully supported by HP.  It is sold that way for small 2-4 node clusters when cost is an issue, although FC has become a big favorite (um...money maker) in recent years.  Yes, SCSI bus resets are a pain, but they are handled by HP-UX, not ServiceGuard.
> 
> --Keith

Hmmm...   Are you sure you're thinking of a multi-initiator _bus_ and
not something like an external SCSI array (i.e. nike arrays or some such
thing)?  I know that multi-port SCSI hubs are available, and more than
one HBA per node is obviously supported for multipathing, but generally
any multi-initiator SCSI setup will be talking to an external raid
array, not a simple SCSI bus, and even then bus resets can cause grief.
Admittedly, I'm much more familiar with the Alpha server side of things
(multi-initiator buses were definitely never supported under DEC unix /
Tru64) , so I could be wrong about HP-ux.  I just can't imagine that a
multi-initiator bus wouldn't be a nightmare.   

-steve


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