In the case of connecting SCSI devices to the Shark, the system to be connected has two SCSI cards and each card is connect to separate SCSI adapters on the Shark. There is also a special driver that needs to be installed (called DPO, dual path option) that handles the multipathing function.
On Thursday 16 May 2002 09:57 am, you wrote: > On Thu, 16 May 2002, Don Mulvey wrote: > > I have heard that multipath i/o is supported on s390 and was curious how > > this is accomplished. If anyone has any information I'd appreciate a > > reference or a reply to this post. > > > > On other architectures, multipath i/o is handled in the scsi layer, > > using the scsi id found on newer drives. However, on a 390 system I > > haven't a clue as to how multipath would be handled ... unless the dasd > > driver is handling it ... but I don't think it does. Can anyone shed > > some light on this? > > Veering slightly OT, just out of curiosity since I know little > about SCSI other than how to set LUNs and the mundanity of cabling SCSI > devices together - > > How do you have "multipath i/o" on SCSI when most devices have > only one parallel cable? (MF devices, particularly large ones often > have two or more slots for "Bus and Tag" connector pairs. > > To answer just a little bit of your question (though Jim Elliot > pointed you to the manuals), the OS doesn't need to know about the > multiple paths. When you add hardware you tell the IOCDS (IO > configuration data set) what channels and controllers reach it; your > engine (CPU) launches an ssch command and the IO subsystem takes over > from there (well you do need to do some setup before the ssch). > Alternately if you're running under VM, your guest may know nothing about > multiple paths to a device but the VM control program (CP) very well may > (or not, leaving it completely to the IO system) - so when CP intercepts > the IO request it may well "think": "H'mm I already have an outstanding > operation through this controller on this channel, but I have another > channel open to this device here so...". > > -- TWZ -- Rich Smrcina Sytek Services, Inc. Milwaukee, WI [EMAIL PROTECTED] [EMAIL PROTECTED] Catch the WAVV! Stay for Requirements and the Free for All! Update your S/390 skills in 4 days for a very reasonable price. WAVV 2003 in Winston-Salem, NC. April 25-29, 2003 For details see http://www.wavv.org
