Calculating PDSE Used Space



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Calculating PDSE Used Space

Postby santlou » Mon Nov 10, 2008 9:34 am

I’m trying work out an algorithm to calculate the Used space of a PDSE.

I obtain the dataset attributes by using a LISTDSI.

When I take the SYSUSEDPAGES and multiply by 4096, this number falls short of the percent utilized
as present in ISPF option 3.2 (Data Set Information). I assume the difference is the space used by
the PDSE directory, but I still can't get an exact match to the Data Set Information.

The Data Set Information is shown below:

                             Data Set Information                         
Command ===>                                                               
                                                                           
Data Set Name  . . . : DOC.CPI.CTLCARD                                 
                                                                         
General Data                         Current Allocation                   
Management class . . : P180Y735      Allocated cylinders : 5           
Storage class  . . . : NOVIO         Allocated extents . : 5           
Volume serial . . . : D1ST38        Maximum dir. blocks : NOLIMIT     
Device type . . . . : 3390                                             
Data class . . . . . : PDSE                                             
Organization  . . . : PO            Current Utilization                 
Record format . . . : FB            Used pages  . . . . : 751         
Record length . . . : 80            % Utilized  . . . . : 83           
Block size  . . . . : 3120          Number of members . : 663         
1st extent cylinders: 1                                               
Secondary cylinders : 1                                               
Data set name type  : LIBRARY                                         
                                                                     
Creation date . . . : 2008/10/18    Referenced date . . : 2008/11/08   
  Expiration date . . : ***None***                                       

Here is the information returned from the LISTDSI for the same dataset:

SYSalloc      5         
SYSused       N/A       
SYSUNIT       3390       
SYSUNITS      CYLINDER   
SYSusedpages  751       
SYSEXTENTS    5         
SYSTRKSCYL    15         
SYSBLKSTRK    N/A       
SYSDSORG      PO         
SYSBLKSIZE    3120       
SYSLRECL      80         
SYSPRIMARY    1         
SYSSECONDS    1         
SYSADIRBLK               
SYSUDIRBLK               
SYSMEMBERS       


For this specific example, this dataset's allocation is 75 tracks (5 cylinders * 15 track/cyl).
I calculated the Used Data space as 3,076,096 bytes by multiplying the SYSUSEDPAGES by 4096 (751 * 4096 = 3076096).

Next, I'm assuming that only full block would fit on one track (a block would not be split on
separate tracks), so a maximum of 13 blocks would fit on one track. The track size on a 3390 is
56664 bytes, so 56664 / 4096 = 13.83. Thus 13 blocks fit on one track. The number of bytes in 13 tracks is 53,248 (13 * 4096 = 53248).

So to determine the Number of Used Tracks, I divide the used dataspace (3076096) by the number of
bytes that fit in full blocks on one track (53248). For this data set I calculated this amount to
be 57.77 tracks (3076096 / 53248 = 57.77 tracks). This works out to about 77% used space. However,
the Dataset Information displays 83% utilized.

Even if we add 3 tracks for the directory space (663 members * 256 bytes per member), the percent
used still does not come close to 83%. Here I'm assuming the directory of a PDSE is 256 bytes per
member. This is probably not accurate for PDSE directory entries (this number - 256 - applies to
PDS directories).

Can anyone point me in the right direction to determining the accurate DASD utilization value of a PDSE? How is the % Used on the Data Set Information screen calculated.

Any assistance would be appreciated.

NOTE: I do not have access to SMF data or IPCS, so I'm limited to information that I can capture through standard REXX calls such as LISTDSI and IDCAMS.
santlou
 
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