Portal | Manuals | References | Downloads | Info | Programs | JCLs | Master the Mainframes
IBM Mainframe Computers Forums Index
 
Register
 
IBM Mainframe Computers Forums Index Mainframe: Search IBM Mainframe Forum: FAQ Memberlist Usergroups Profile Log in to check your private messages Log in
 

 

Allocate dataset withour BLKSIZE

 
Post new topic   Reply to topic    IBMMAINFRAMES.com Support Forums -> CLIST & REXX
View previous topic :: :: View next topic  
Author Message
Susanta

Active User


Joined: 17 Nov 2009
Posts: 122
Location: India

PostPosted: Thu Sep 22, 2016 11:51 am    Post subject: Allocate dataset withour BLKSIZE
Reply with quote

Hi

I need to allocate a file within rexx code,
Need to if i can ommit the block size filed,
what are the impacts of not providing blksize.

Code:
"ALLOC F(OUTDD) DA('"DSN1"') ",                           
"NEW CATALOG LRECL(80)  RECFM(F B) DSORG(PS)",
"SPACE(10 5) TRACKS UNIT(SYSDA) "                       



Thanks
Back to top
View user's profile Send private message

Abid Hasan

New User


Joined: 25 Mar 2013
Posts: 85
Location: India

PostPosted: Thu Sep 22, 2016 12:33 pm    Post subject: Reply to: Allocate dataset withour BLKSIZE
Reply with quote

Hello,

But you do not have 'BLKSZ' specified in the snippet shown.
Nevertheless, REXX or otherwise - block size is for a dataset and it tells the system how/how-much data is to be arranged in storage blocks, so the same rules that apply to your normal JCL (where you'd specify a NEW/CATLG, and other definitions parameters, including/excluding BLKSIZE) apply here as well. If you specify a block-size for a DS, then you force the system to comply to certain 'storage rules', if not calculated correctly for a DS having large number of records (read > a mill. records), and say the DS is processed sequentially in batch, you might end up impacting the EXCPs used, CPU used, might end up increasing the clock-time as well; and vice-versa. General recommendation states, skip coding block-size and let system decide it for you - until and unless you're very sure of the number you want to punch in.

PS: Should you choose to calculate the number, do bear in mind the LRECL/Space allocation/expected-number-of-records for the DS as well; you can read more about block-size in the JCL Reference and DFSMS manuals; more information in 'Using Data Sets' manual.
Back to top
View user's profile Send private message
steve-myers

Active Member


Joined: 30 Nov 2013
Posts: 516
Location: The Universe

PostPosted: Thu Sep 22, 2016 4:12 pm    Post subject:
Reply with quote

When you allocate a data set as you did here specifying DSORG(PS), using space unit as CYLINDER or TRACK and specifying the RECFM and LRECL, allocation will compute the appropriate system determined BLKSIZE and apply it to the data set.

I have two other observations.
  • Why are you asking here? You can find out yourself by just executing a LISTD command. For example -
    Code:
    alloc da(test1) sp(1) tra dsorg(ps) recfm(f b) lrecl(80)
     READY                                               
    listd test1
     XXXXXX.TEST1
     --RECFM-LRECL-BLKSIZE-DSORG
       FB    80    27920   PS
     --VOLUMES--
       VVVVVV
     READY
    There are other ways, of course, but this uses the TSO command line,
  • When you allocate a data set using the ALLOCATE command, the data set will remain allocated to your session until you free it using the FREE DATASET(xxx) command or you logoff
Back to top
View user's profile Send private message
View previous topic :: :: View next topic  
Post new topic   Reply to topic    IBMMAINFRAMES.com Support Forums -> CLIST & REXX All times are GMT + 6 Hours
Page 1 of 1

 

Search our Forum:

Similar Topics
Topic Author Forum Replies Posted
No new posts Fileaid 2 commands instream work. In ... descann Compuware & Other Tools 2 Tue May 16, 2017 3:31 pm
No new posts To find out size allocated to a seque... ashek15 JCL & VSAM 15 Thu Apr 27, 2017 9:42 am
No new posts LISTCAT on a dataset with symbolic pa... shreya19 JCL & VSAM 5 Fri Apr 07, 2017 5:43 pm
No new posts Unable to catalog a gdg dataset resid... Shovan JCL & VSAM 7 Fri Mar 24, 2017 2:24 pm
No new posts Want to pull the job log into a Mainf... Jishu Mukherjee Compuware & Other Tools 9 Tue Mar 21, 2017 4:48 pm


Facebook
Back to Top
 
Mainframe Wiki | Forum Rules | Bookmarks | Subscriptions | FAQ | Tutorials | Contact Us