𝗪𝗵𝘆 𝗗𝗦𝗟𝗜𝗦𝗧(𝟯.𝟰) 𝗥𝗲𝗽𝗼𝗿𝘁𝗲𝗱 𝟲% 𝗮𝗻𝗱 𝟯% 𝗨𝘁𝗶𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 𝗼𝗻 𝗙𝘂𝗹𝗹𝘆 𝗢𝗰𝗰𝘂𝗽𝗶𝗲𝗱 𝗠𝘂𝗹𝘁𝗶-𝗩𝗼𝗹𝘂𝗺𝗲 𝗗𝗮𝘁𝗮𝘀𝗲𝘁𝘀: 𝗔 𝗗𝗙𝗦𝗢𝗥𝗧 𝗜𝗻𝘃𝗲𝘀𝘁𝗶𝗴𝗮𝘁𝗶𝗼𝗻

The below dataset spans four volumes, yet DSLIST reports utilization values of only 6% and 3% for the first two volumes. Since sequential datasets normally fill earlier volumes before extending to additional volumes, these figures appeared anomalous and warranted further investigation.

The following DSLIST 3.4 output shows the dataset allocation across four volumes.

Command - Enter "/" to select action                  Message           Volume
      Tracks  %     XT Device  Dsorg Recfm Lrecl Blksz  Created    Referred   
-------------------------------------------------------------------------------
         XY67890.PRODHIST.ORDRARCH.BACK.DATA                             XXX710
       69745   6    16 3390     PS   FB      228 27816 2026/08/07 2026/08/07  
-------------------------------------------------------------------------------
         XY67890.PRODHIST.ORDRARCH.BACK.DATA                             XXX674
       67860   3    11 3390     PS   FB      228 27816 2026/08/07 2026/08/07  
-------------------------------------------------------------------------------
         XY67890.PRODHIST.ORDRARCH.BACK.DATA                             XXX612
       60320 100    14 3390     PS   FB      228 27816 2026/08/07 2026/08/07  
-------------------------------------------------------------------------------
         XY67890.PRODHIST.ORDRARCH.BACK.DATA                             XXX678
       60320  93    11 3390     PS   FB      228 27816 2026/08/07 2026/08/07  
 
                             Data Set Information                            
                                     
 Data Set Name . . . . : XY67890.PRODHIST.ORDRARCH.BACK.DATA            
                                                                        
 General Data                          Current Allocation              
  Management class . . : XXXACTX        Allocated megabytes : 13,701   
  Storage class  . . . : XXXX           Allocated extents . : 52       
   Volume serial . . . : XXX710 +                                      
   Device type . . . . : 3390                                          
  Data class . . . . . : DCXXXXX                                       
   Organization  . . . : PS            Current Utilization             
   Record format . . . : FB             Used megabytes  . . : 6,532    
   Record length . . . : 228            Used extents  . . . : 2        
   Block size  . . . . : 27816                                         
   1st extent megabytes: 100                                           
   Secondary megabytes : 400           Dates                           
   Data set name type  :                Creation date . . . : 2026/08/07
   Data set encryption : NO             Referenced date . . : 2026/08/07
                                        Expiration date . . : ***None***
 
The following DFSORT job was used to determine how records are distributed across the dataset's four volumes.
 
The first DFSORT step reads the entire dataset and provides the total record count. Subsequent DFSORT steps specify VOL=(,,2), VOL=(,,3), and VOL=(,,4), causing processing to begin from the second, third, and fourth volume respectively. By subtracting the resulting record counts, the number of records residing on each individual volume can be derived.
 
 
//STEP010  EXEC PGM=SORT                                         
//SORTIN   DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA,DISP=SHR    
//SORTOUT  DD DUMMY                                              
//SYSOUT   DD SYSOUT=*                                           
//SYSIN    DD *                                                  
  SORT FIELDS=COPY                                               
//*                                                              
//STEP020  EXEC PGM=SORT                                         
//SORTIN   DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA,DISP=SHR,   
//            VOL=(,,2)                                          
//SORTOUT  DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL2,   
//            DISP=(,CATLG),                                     
//            SPACE=(1,(200,200),RLSE),AVGREC=M                  
//SYSOUT   DD SYSOUT=*                                           
//SYSIN    DD *                                                  
  SORT FIELDS=COPY                                               
//*                                                              
//STEP030  EXEC PGM=SORT                                         
//SORTIN   DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA,DISP=SHR,   
//            VOL=(,,3)                                          
//SORTOUT  DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL3,   
//            DISP=(,CATLG),                                     
//            SPACE=(1,(200,200),RLSE),AVGREC=M                  
//SYSOUT   DD SYSOUT=*                                         
//SYSIN    DD *                                                
  SORT FIELDS=COPY                                             
//*                                                            
//STEP040  EXEC PGM=SORT                                       
//SORTIN   DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA,DISP=SHR, 
//            VOL=(,,4)                                        
//SORTOUT  DD DSN=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL4, 
//            DISP=(,CATLG),                                   
//            SPACE=(1,(200,200),RLSE),AVGREC=M                
//SYSOUT   DD SYSOUT=*                                         
//SYSIN    DD *                                                
  SORT FIELDS=COPY                                             
//*                                                            
 
Below is the SYSOUT of each step
 
SORTIN   : RECFM=FB   ; LRECL=   228; BLKSIZE= 27816  
SORTIN   : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA    
SORTOUT  : DSNAME=NULLFILE                            
RCD IN   62025525, OUT   62025525 
 
SORTIN   : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA        
SORTOUT  : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL2
RCD IN   45007745, OUT   45007745 
 
SORTIN   : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA           
SORTOUT  : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL3  
RCD IN   28449905, OUT   28449905 
 
SORTIN   : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA         
SORTOUT  : DSNAME=XY67890.PRODHIST.ORDRARCH.BACK.DATA.SNGLVOL4
RCD IN   13731825, OUT   13731825 
 
Record Distribution Across Volumes
 

Volume	Record Count Calculation	Records in Volume
XXX710 (Vol 1)	62,025,525 − 45,007,745	17,017,780
XXX674 (Vol 2)	45,007,745 − 28,449,905	16,557,840
XXX612 (Vol 3)	28,449,905 − 13,731,825	14,718,080
XXX678 (Vol 4)	Remaining Records	13,731,825

 
Dataset Size and Track Usage Calculation
 

Volume	Dataset Size (Bytes)	Track Calculation	Tracks Used
XXX710(Vol 1)	3,880,053,840	3,880,053,840 ÷ (2 × 27,816)	69,745
XXX674(Vol 2)	3,775,187,520	3,775,187,520 ÷ (2 × 27,816)	67,860
XXX612(Vol 3)	3,355,722,240	3,355,722,240 ÷ (2 × 27,816)	60,320
XXX678(Vol 4)	3,130,856,100	3,130,856,100 ÷ (2 × 27,816)	56,278

 
Formula Used
Dataset Size (Bytes) = Records × LRECL
Tracks Used = Dataset Size ÷ (2 × BLKSIZE)
 
where:
LRECL = 228
BLKSIZE = 27816
 
DSLIST vs. DFSORT Comparison of Volume Utilization
 

Volume	DSLIST Tracks	DSLIST Used %	Calculated Tracks Used (DFSORT)	Comparison
XXX710	69,745	6%	69,745	Exact match
XXX674	67,860	3%	67,860	Exact match
XXX612	60,320	100%	60,320	Exact match
XXX678	60,320	93%	56,278	Close match. 60,320 × 93% = 56,098 tracks, which is very close to the calculated value of 56,278 tracks

 
 
Conclusion
 
Although DSLIST reports utilization values of only 6% and 3% for volumes XXX710 and XXX674, DFSORT analysis confirms that both volumes are effectively 100% utilized by dataset data. The calculated track usage matches the DSLIST track counts exactly, demonstrating that the reported percentages are misleading and do not reflect the actual occupancy of these volumes. 

For basic format sequential datasets, the maximum number of tracks that can be addressed on a single volume is 65,535. When DSLIST encounters an allocation that exceeds this limit, it appears to calculate the utilization percentage using only the tracks beyond 65,535.

• Volume XXX710: 69,745 tracks allocated
• Excess tracks = 69,745 − 65,535 = 4,210
• DSLIST reported utilization = 4,210 / 69,745 ≈ 6%
• Volume XXX674: 67,860 tracks allocated
• Excess tracks = 67,860 − 65,535 = 2,325
• DSLIST reported utilization = 2,325 / 67,860 ≈ 3%

As a result, DSLIST displays 6% and 3% utilization for the first two volumes even though those volumes are effectively full. The percentages reflect only the tracks beyond the 65,535-track threshold rather than the actual space utilization of the volumes.

The dataset XY67890.PRODHIST.ORDRARCH.BACK.DATA is a basic-format sequential dataset. According to IBM documentation,https://www.ibm.com/docs/en/zos/2.1.0?topic=set-types-dasd-sequential-data-sets, a basic-format sequential dataset on a single volume is limited to a maximum of 65,535 tracks.

However, the system appears to allow allocations that exceed this documented limit. This behavior may indicate a z/OS or SMS defect.