Calculating space for a PDS with 100 members

vignesh subramanian · New User Joined: 08 May 2009 Posts: 2 Location: Bangalore

Hi!

A PDS should hold 100 members, each member having a maximum capacity of 50,000 records. Record length is 200 bytes each.

what minimum primary, secondary and directory values should be assigned in the SPACE parameter when allocating this PDS?

SPACE (CYL,(?,?,?))

Thanks
VS

Robert Sample · Posted: Thu Jul 09, 2009 1:26 am

What did you calculate?

ISPF statistics or not?

vignesh subramanian · New User Joined: 08 May 2009 Posts: 2 Location: Bangalore

I referred to the last post in the below link to calculate the number of cylinders, but not sure of the value for directory

www.ibmmainframes.com/about24595.html

See my calculation below.

27998 / 200 = 13900, which is the optimum blocksize for a 3390 DASD.
This means that we get 139 records per block and two blocks on each
track. So 279 records on each track.

50,000 / 279 = 179.21 (rounded up to) 180 tracks of used space.

= 18,000 tracks for 100 members

180 / 15 = 12 cylinders of used DASD space.

= 1,200 cylinders for 100 members

enrico-sorichetti · Posted: Thu Jul 09, 2009 2:19 am

Your computations ( at least the intermediate steps) are a few bytes off
( even if You get the right results because of rounding )

for 3390 here are the exact figures

the best blksize for your case ( LRECL=200 ) is 27800 ( edited to correcta typo )
which gives 2 blocks per track for 278 record per track
which for a 50000 records for each member gives 50000 / 278 = 179.8561 tracks
which rounded gives 180 tracks for each member or 12 cylinders ( at 15 tracks per cylinder )
which gives 1200 cylinders ( for 100 members )

as far as the directory blocks are concerned ( for a PDS - not a PDSE )
see this post for the computation details
www.ibmmainframes.com/viewtopic.php?t=29878

with ispf statistics You will need
100/6 ==> 17 directory blocks

allocating in cylinders You should specify something along...
SPACE=(CYL,(1201,1200,44)) 1 track of directory blocks
the secondary allocation is arbitrary, for Your estimates, it allows one edit and replace for each member

expat · Posted: Thu Jul 09, 2009 11:22 am

With directory blocks I always do my allocations in tracks.

The last track will hold only 44 blocks, where all others 45, so to fully utilise the track I use, 44,89,134,................ starting with 44, and then incrementing by 45