OSAM Multi Volume Allocations
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#1: OSAM Multi Volume Allocations Author: ajdeaver, Location: St. Paul Minnesota PostPosted: Wed Apr 30, 2003 2:40 pm
    —
Two ways to allocate a multi-volume file within an SMS environment:

Code:

//ALLOCATE EXEC PGM=IEFBR14                                   
//ROSLOAD  DD DSN=INDV.TCISS.DB.SEPACC1.JEFF,                 
//         STORCLAS=SCADMIN,                                 
//         DISP=(NEW,CATLG),                                 
//         VOL=SER=(CPY031,CPY036,CPY037,CPY027),             
//         DCB=(DSORG=PS,RECFM=FBS,BLKSIZE=22428,LRECL=22428),
//         SPACE=(CYL,(50,100)),UNIT=DISK                   


and this one...

Code:

//ALLOCATE EXEC PGM=IEFBR14                             
//DD02     DD DISP=(NEW,CATLG),DCB=(DSORG=PS),           
//         UNIT=DISK,VOL=SER=(CPY031),STORCLAS=SCADMIN, 
//         SPACE=(CYL,(50,5)),                           
//         DSN=INDV.TCISS.DB.SEPACC1.JEFF               
//DD03     DD DISP=(MOD,KEEP),DCB=(DSORG=PS),           
//         UNIT=DISK,VOL=SER=(CPY036),STORCLAS=SCADMIN, 
//         SPACE=(CYL,(50,5)),                           
//         DSN=INDV.TCISS.DB.SEPACC1.JEFF               
//DD04     DD DISP=(MOD,KEEP),DCB=(DSORG=PS),           
//         UNIT=DISK,VOL=SER=(CPY037),STORCLAS=SCADMIN, 
//         SPACE=(CYL,(50,5)),                           
//         DSN=INDV.TCISS.DB.SEPACC1.JEFF               
//DD05     DD DISP=(MOD,KEEP),DCB=(DSORG=PS),           
//         UNIT=DISK,VOL=SER=(CPY027),STORCLAS=SCADMIN, 
//         SPACE=(CYL,(50,100)),                         
//         DSN=INDV.TCISS.DB.SEPACC1.JEFF               


I'm being told by my IMS DBA that the first one does not work for his OSAM datasets, that only the second will do. Can anyone explain to me the difference between the results of these allocations as they look to be the same to me.

SCADMIN is a storage class we have defined with the guarenteed space attribute turned on.
#2:  Author: Mike, Location: Sydney, Australia PostPosted: Mon May 12, 2003 10:35 pm
    —
Although I'm not sure I think that the latter method creates dataset extents on each of the volumes these could be virtually be classed as seperate datasets. The first method will only expand into extents if insufficient space exists on the first volume. I think that IMS uses the additional extents for stroring overflow data which could exist even if the primary extent doesn't need expanding.
#3:  Author: Bithead, Location: Michigan, USA PostPosted: Tue May 13, 2003 9:57 am
    —
OSAM dataset allocation has a quirk that can put an end-of-file marker on the first physical dataset that makes the rest of the dataset unuseable.

I used to split my databases across multiple volumes for performance reasons but I have dropped that technique with the faster, cached DASD. The JCL to build the database would allocate but not catalog each extent. An additional step would then catalog them together.
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