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 -- Linux-cluster@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/linux-cluster
