SCSI cable problem .

ITEM: RTA000069533

We need to connect one 3514-213, one 7208(5GBy) and one 9348 to two             
machines simultaneously  one RISC System 6000 Model 380 and                     
one Model 250.                                                                  
We plan to use the devices from only one machine at the same time.              
We plan to connect the 3514-213 using SCSI-2 F/W diff adapters                  
in each machine . With Y cables in each adapter in order to share               
the 3514.                                                                       
Our problem is we need to share the tapes too.                                  
Is there some way to connect the tapes to the shared SCSI-2 F/W DIFF            
interface without affecting the capability to share 3514?                       
If the answers is no, is there a way to share the tapes devices using           
the integrated scsi units of both  machines?                                    
Could you tell me which cables are needed?                                      
   The 3514-213 is currently not supported in a twin-tailed environment.        
   The cabling for a twin-tailed 3514 configuration has not yet been            
   tested.  The 3514-213 has not been tested in a multi-initiator               
   environment (HACMP or no HACMP), so the results of this                      
   configuration are not predictable.                                           
   In theory, you can connect the 3514-213 as described, however, if            
   you run into problems, this twin-tailed configuration is not                 
   supported by IBM.                                                            
   In a non-twin-tailed environment, AIX will allow one system to               
   control the 3514-213 by importing and varyon the volume group.              
   This has not been tested in twin-tailed environment with the                 
   3514-213, however, IN THEORY, it could work to allow one system              
   to control the device at a time.  But again, this is not supported           
   by IBM currently.                                                            
   It is NOT possible to connect the twin-tailed tape drives to the             
   integrated SCSI interfaces on the 250 and the 380.  There are                
   several reasons for this:                                                    
   o  The 250 has an integrated SCSI-2 Fast/Narrow (8-bit) connector,           
      50-pin interface.  This adapter does not support twin-tailing             
      because you cannot remove the adapter termination.  In standard           
      twin-tailing configurations, you MUST remove adapter internal             
      SCSI termination because either the PTT or Y-Cables will provide          
      SCSI bus termination.  PTT and Y-Cables have a termination point          
      built in.  Thus, cabling the 8-bit Y-Cable (this cable has a             
      50-pin interface) to the 250 integrated SCSI-2 will at least              
      result in a "triply" terminated SCSI bus (not considering the             
      380's integrated adapter).                                                
   o  More than 2 terminators on a SCSI bus will NOT work.                      
      NOTE:  The PTT Cables CANNOT be connected to the 250's integrated         
      SCSI-2 50-pin interface, because PTT cables have 60-pin                   
      connectors.  PTT cables are supported with the SCSI-1 SE and              
      SCSI-2 8-bit SE external Micro Channel adapters.                          
   o  The 380 has an integrated SCSI-2 F/W connector.  This can                 
      be cabled to have an 8-bit bus, however, this adapter does                
      not support twin-tailing.  The internal termination cannot                
      be moved to an outside point.  So, with the 250 integrated                
      controller and Y-cables, this configuration would result in a             
      4-times-terminated SCSI bus.  This will NOT work.                         
   o  NOTE:  PTT cables CANNOT be used on the 380's integrated                 
      SCSI-2 F/W connector, even with the 8-bit converter.                      
   o  Twin-tailing on integrated SCSI adapters is not supported                 
      because it WILL NOT WORK.                                                 
   ISSUES ON SHARING TAPES DRIVES:                                              
   o  IBM does not support twin-tailing these tape drives.  The                 
      integrated SCSI adapters on the 250 and 380 are not suitable              
      for twin-tailing any device.  You would require EXTERNAL                  
      SCSI-1 SE adapters (with no internal SCSI devices) and PTT                
      cables, OR Micro Channel SCSI-2 F/W 8-bit SE adapters and                 
      8-bit Y-Cables to achieve a workable twin-tailed solution.                
      o  No mixing PTT and Y-cables on the same bus.                            
      o  This solution is NOT supported or tested by IBM.                       
   o  AIX assumes that only one system owns a tape drive.  AIX cannot          
      manage tape drives to intelligently handle concurrent attempts            
      to access the device.  Tape drive access would have to be                 
      monitored by a third party software or manually managed through           
      AIX commands (i.e. making the device "Available" to only one              
      system at a time).                                                        
   o  IBM does not provide or support SCSI switches that will permit            
      shared tape operation between two systems.                                
   o  You may wish to investigate the SYSBACK/6000 offering as a                
      possible supported solution.  This offering will allow                    
      customers to backup/restore data to/from a remote tape drive.             
      Only one system is attached to (or "owns") the tape drive.                
      For additional details about SYSBACK, please refer to the                 
      SWAPPLIC application on HONE, product number 5764-047.                    
S e a r c h - k e y w o r d s:                                                 

WWQA: ITEM: RTA000069533 ITEM: RTA000069533
Dated: 06/1996 Category: ITSAI6000HW
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