Difference b/w UNIT, VOLUME and SERIAL in JCL

tyln · New User Joined: 19 Mar 2005 Posts: 1

what is the difference in UNIT, VOLUME and SERIAL in JCL?

subhasis_50 · Moderator Joined: 09 Mar 2005 Posts: 367 Location: Earth

Hi,
UNIT parameter must be taken into consideration if any other facility is not supplying the information for example SMS. This is used with Dataset.
It can be one of the following:

DEVICE ADDRESS: A 3 or 4 digit Hexadecimal address of the device being requested.

DEVICE TYPE: Request a device by its generic name, supplied by IBM

GROUP NAME: Request a group of device with a symbolic name which is assigned during the time of system generation or IBM supplied.

UNIT COUNT: Specifies the no of the devices requested for a particular dataset.

DEFER: Request that the volume not be mounted until the dataset is opened.

AFFINITY: Request that the system allocates different datasets residing on different removable volumes to the same device during the execution of a step.

For Example:
UNIT=DISK
UNIT=TAPE
UNIT=SYSDA etc

VOLUME: It can request a specific volume by means of the serial no, or by requesting the same volume used by another dataset, or can refer back to a previous DD statement.

Example:
//DD1 DSN=TEMP.FILE,DISP=OLD, UNIT=SYSDA,
// VOL=SER=PACK1

//DD2 DSN=TEMP1.FILE,DISP=(NEW,CATLG,DELETE),UNIT=DISK,
// VOL=REF=TEMP.FILE

//DD3 DSN=TEMP2.FILE,DISP=OLD,UNIT=333,
// VOL=REF=*.DD1

SERIAL: Serial is used for referring the requested volume by using the serial no. See the first ex mentioned above.
Hope it will help

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1503

To put it another way: The VOLUME is the medium upon which you put the data. A UNIT is where the VOLUME(s) reside(s). The SERIAL is the name of the VOLUME(s).