Concerns when viewing HFS data set statistics

Some of the information about an HFS data set is maintained within the data set itself and not in the VTOC, VVDS, or catalog. For example, information about the number of members, percent utilization, and used pages, is kept within the data set. The HFS data set must be mounted for this information to be gathered and displayed. Common interfaces are the DCOLLECT function under DFSMS, the Info action in ISPF with the DSLIST function, ISPF 3.4, or ISPF 3.2. If the HFS data set is not already mounted, an implicit mount is performed to allow DFSMS to gather the requested internal statistics; the data set is unmounted once the function is completed.

Some potential pitfalls:
- The requester for HFS data set statistics has no OMVS segment; the security program fails the request.
- The HFS that contains the requester's HOME directory (refer to the OMVS segment for the requester) is quiesced. The most likely cause for a file system to be quiesced is for a logical dump or copy operation; a file system can also be quiesced by command from a REXX exec. This causes latch contention for the file system latch; below are displays from an example. In this example, userid MEGA has a HOME of '/u'; the file system currently mounted at '/u' is quiesced. This causes user MEGA to hang when doing ISPF 3.4/I on any HFS data set while the POSIX.HFS.MEGA HFS data set is quiesced.

                             
D OMVS,F                                                                
BPXO045I 10.52.04 DISPLAY OMVS 247                                      
OMVS     000D ACTIVE          OMVS=(ZF)                                 
TYPENAME   DEVICE ----------STATUS----------- MODE                      
HFS            13 QUIESCED                    RDWR                      
  NAME=POSIX.HFS.MEGA                                                   
  PATH=/u                                                               
  QSYSTEM=SY1 QJOBNAME=MEGA QPID=  83886087                             
                                                                        
D GRS,C                                                                
ISG343I 10.52.29 GRS STATUS 252                                         
NO ENQ RESOURCE CONTENTION EXISTS                                       
LATCH SET NAME:  SYS.BPX.A000.FSLIT.FILESYS.LSN                         
CREATOR JOBNAME: OMVS      CREATOR ASID: 000D                           
  LATCH NUMBER:  22                                                     
    REQUESTOR  ASID  EXC/SHR    OWN/WAIT                                
    MEGA       0021  EXCLUSIVE  OWN                                     
    MEGA       0021  SHARED     WAIT      

In this case, the contention can be relieved by waiting for the quiesce requestor to complete or by unquiescing the file system from another user.