Differences of Primary/Copy Volumes vs. Dual Primary Volumes

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Differences of Primary/Copy Volumes vs. Dual Primary Volumes

The typical CA Disk backup/archive process creates duplicate outputs on tape or disk referred to as the primary and copy archive volumes (or, ARCHVOLS).

An optional process that can be utilized during backup/archive is to create Dual Primary Volumes. Using this option, the backup/archive process creates PRIMARY1 and PRIMARY2 (P1 and P2) volumes on tape or disk.

Here are some distinctions between these two processes:

Primary/Copy	Dual Primary Volumes
The primary and copy volumes contain exactly the same data.	The two primary volumes contain exactly the same data.
The primary/copy volume relationship does not change for the life of the volumes.	The P1 and P2 volumes are not connected or related in any way.
For each data set processed, one DSNINDEX record is created.	For each data set processed, a P1 DSNINDEX record and a P2 DSNINDEX record is created.
A primary ARCHVOLS and a copy ARCHVOLS record are created for the output volumes.	A P1 ARCHVOLS record is created for the P1 output volume and a P2 ARCHVOLS record is created for the P2 output volume.
The DSNINDEX record contains the volser (or key) of the primary ARCHVOLS record.	The P1 DSNINDEX record contains the volser (or key) of the P1 ARCHVOLS record and, the P2 DSNINDEX record contains the volser (or key) of the P2 ARCHVOLS record.
The primary ARCHVOLS record contains the key of the copy ARCHVOLS record.	The P1 ARCHVOLS record has no field pointing to the P2 ARCHVOLS record, nor does the P2 ARCHVOLS record point to the P1 ARCHVOLS record.
The primary and copy archvol cannot be managed separately.	The P1 DSNINDEX and P1 ARCHVOLS records can be managed independently of the corresponding P2 records.
The copy ARCHVOL is kept until the primary ARCHVOL expires, at which time the copy ARCHVOL is also expired.	The P2 DSNINDEX and P2 ARCHVOLS records can expire before, after or at the same time as the P1 records.

In an execution of CA Disk, the option to create Dual Primary Volumes can be utilized or Primary/Copy volumes can be created. These are mutually exclusive processes in the job step being executed. The Copy Utility can be used to create copies of the Dual Primary Volumes.

All of the P1 and P2 DSNINDEX and ARCHVOLS records are maintained in the FILES, along with the entries for the primary/copy ARCHVOLS and DSNINDEX records.
The DSNINDEX records and the primary ARCHVOLS records created in the primary/copy process are considered as P1 records (for example, the P2 indicator flag is off).

There is no distinction - and no method to distinguish - between primary DSNINDEX records and ARCHVOLS created in the primary/copy process and the P1 DSNINDEX records and ARCHVOLS created in the Dual Primary Volume process.

Although the Dual Primary Volume feature provides very flexible options in managing dual output images and volumes, the user must be aware that there can be a significant increase in the number of DSNINDEX records maintained in the FILES data set.

Before using the Dual Primary Volume feature, the following factors must be considered when using an FDS:

Ensure that the physical size (number of cylinders allocated) of the FDS is adequate to contain the expected increase of DSNINDEX records.
Ensure that the record (or, indexing) capacity for the DSNINDEX subfile is adequate (specified in member FILEDEFN in the CA Disk PARMLIB).
The runtime of IXMAINT can be longer because of the additional records created by this feature.