Preallocating space for multivolume data sets

This topic shows scenarios for preallocating space for multivolume data sets.

Allocating a multivolume data set on SMS-selected volumes

The following JCL allocates a multivolume data set on SMS-selected volumes. The storage class DBLOG must have Guaranteed Space=Y. This example allocates 100 MB on each of five volumes. When all of the allocated space is used for the data set on one volume, the secondary space is allocated as required in extents on that volume. For example:

//DD1  DD  DSN=ENG.MULTFILE,DISP=(,KEEP),STORCLAS=DBLOG,
//         SPACE=(1,(100,25)),AVGREC=M,
//         UNIT=(3380,5)

Note:

After 100 MB is used on the first volume, 25 MB extents of secondary space is allocated on it until the extent limit is reached or the volume is full.
If more space is needed, 100 MB of primary space is used on the second volume. Then, more secondary space is allocated on that volume.
The same process is repeated on each volume, as shown in Figure 1.

Figure 1. Allocation of Primary and Secondary Space for Multivolume Data Sets

Allocating a multivolume data set with different primary allocation on each volume

The following JCL allocates a multivolume data set on SMS-selected volumes with different primary allocation on each volume. The storage class DBLOG must have Guaranteed Space=Y. This example preallocates 10 cylinders on the first volume (VOL1), 20 cylinders on the second volume (VOL2) and 30 cylinders on the third volume (VOL3). When all of the primary space is used on a volume, the secondary space is allocated as required in extents on that volume. For example:

//DD1 DD DSN=DATASET1,DISP=(MOD,CATLG),SPACE=(CYL,(10,5)),VOL=SER=VOL1
//DD2 DD DSN=DATASET1,DISP=(MOD,CATLG),SPACE=(CYL,(20,5)),VOL=SER=VOL2
//DD3 DD DSN=DATASET1,DISP=(MOD,CATLG),SPACE=(CYL,(30,5)),VOL=SER=VOL3

Note:

After the 10 preallocated cylinders are used on VOL1, 5 cylinder extents of secondary space are allocated on this volume until the extent limit is reached or the volume is full.
If more space is needed, the 20 cylinders of preallocated primary space is used on VOL2. Secondary space is allocated on this volume, as required, until the extent limit is reached or the volume is full.
If more space is needed, the 30 cylinders of preallocated primary space is used on VOL3. Secondary space is allocated on this volume, as required, until the extent limit is reached or the volume is full.

Figure 2. Allocation of Primary and Secondary Space for Multivolume Data Sets with Different Primary Allocations on Each Volume

Allocation of primary and secondary space for multivolume data sets with different primary allocations on each volume: The primary space increases from volume 1 to volume 2 and from volume 2 to volume 3. The secondary space and space for other data sets remains constant.