Sharing 7133 ssa disks

ITEM: RS4000016710

Question:                                                                       
  We have the following HW configuration:                                       
  SP/2 with several nodes.  Always two nodes share one 7133 SSA disk            
  drawer. AIX Ver. 4.1.4                                                        
  Node 1 has hdisk2, hdisk3, hdisk4 of the 7133 in his volume                   
  group node1vg.                                                                
  Node 2 has hdisk5, hdisk6, hdisk7 of the 7133 in his volume                   
  group node2vg. (two separate loops)                                           
  When the volume group node1vg on node 1 is varied off properly,               
  I can import node1vg into node 2 and the same is working.                     
  vice versa.                                                                   
  I case node 1 crashes and therefore the volume group wasn't varied            
  off                                                                           
  properly, it's not possible to import node1vg into node 2. We get             
  SSA_LINK_OPEN errors and device busy messages.                               
  Is it possible to import a volume group under such circumstances              
  without using HACMP ?                                                         
                                                                                
Answer..........:                                                               
  Sharing disks between more than one system is only officially                 
  supported                                                                     
  using HACMP, for the reason you have found in your test. Even though          
  SSA disks are not SCSI, they still use the SCSI command set for their         
  interface. As with other SCSI disks, when a volume group is varied on         
  to a system, that system puts a SCSI RESERVE on the disks in the              
  volume                                                                        
  group. Varying the volume group off releases the SCSI RESERVE, making         
  the volume group available for access by other systems. If the system         
  crashes abnormally though, without being able to vary off the volume          
  group, the RESERVE remains on the disks, and other systems can't             
  access                                                                        
  them. This is why you couldn't import the volume group (or if you had         
  previously imported it, you wouldn't be able to vary it on). Powering         
  off and then powering back on the disks in question should remove the         
  RESERVE and allow them to be imported.                                        
                                                                                
  HACMP has special code in its takeover scripts to break this RESERVE          
  condition in this case, and so is the only environment that is                
  officially supported for sharing disks.                                       
                                                                                
S e a r c h - k e y w o r d s:                                                  
WRM  aix                                                                        
                                                                                
                                                                                
                                                                               



WWQA: ITEM: RS4000016710 ITEM: RS4000016710

Dated: 12/1997 Category: AIXOPSUP

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