The PAN#4 ++CLEAR command formats disk files for subsequent use as a CA Panvalet library.
This section covers the following topics:
++CLEAR [RECORDS=nn] [,DATASETS=nnnnnn]
Use this optional parameter to specify the number of records per track for the library. It also determines the corresponding block size. The value must be valid for the type of DASD device used. (For more information, see Table of Block Sizes in this chapter.) For FBA devices, this is the number of 512-byte blocks per control interval. The maximum value is 64 for FBA devices.
If this parameter is omitted or incorrect (RECORDS=00), a default block size is automatically selected for the device being used. For FBA devices, the default is 8.
You must include the CLEAR command in a PAN#4 execution as the first statement in the input stream. If you code both parameters, you must separate them by a comma, but you can code them in any order.
This topic describes the characteristics and capacity of the CA Panvalet library and further explains the two parameters of the CLEAR command.
A CA Panvalet library can contain a maximum of 131,071 physical blocks. The amount of DASD space allocated in the job control for PAN#4 and the number of blocks/track optionally specified in the PAN#4 CLEAR command, RECORDS=nn, determines the number of physical blocks allocated to a library. The number of physical blocks equals the number of tracks multiplied by the number of blocks/track.
The number of physical blocks determines the maximum number of members you can store on the library. Several other factors determine the number of members you can store. The first rule is: the maximum number of members cannot exceed the number of physical blocks allocated. The theoretical maximum is 131,071 members.
The block size can range from 502 bytes to 32K. In selecting a block size, first consider the amount of machine storage available for executing the CA Panvalet programs. As a general rule, add twice the library block size to the base storage size of each program.
Generally, if storage is not a problem, specify a large block size. The large block size maximizes the storage capacity of the DASD device, whereas a smaller block size means some loss in storage due to inter-record gaps (true of all DASD files). CA Panvalet stores only one member in a block. Therefore, the chosen block size should not greatly exceed the average compressed space anticipated for most members. Too large a block size wastes considerable disk space.
Physical blocks allocated to the library are divided into two types: overhead blocks and data blocks. Overhead blocks contain the directory entries and control information. Data blocks (physical blocks minus overhead blocks) are used for the storage of the library members. The number of overhead blocks is dynamically allocated based on the block size and the number of directory entries desired.
In the CLEAR command, you can optionally specify an estimated number of library members to be stored (DATASETS=nnnnnn). PAN#4 then allocates the approximate number of overhead blocks required to represent that many directory entries. If you do not specify a value, PAN#4 allocates one directory entry for every three data blocks.
It is to your advantage to specify an estimated number of library members (DATASETS=nnnnnn) if additional directory entries are required.
Overhead blocks and data blocks are not interchangeable after the allocation has taken place. In the event overhead blocks are all in use, data blocks are not made available. If data blocks are all in use, overhead blocks are not made available. In these situations, the appropriate error message is generated. To resolve the problem, you must reallocate the library, incorporating the needed change.
Code the CLEAR command as follows to clear and format 6000 tracks on a 3330 pack using a block size of 2498 (five blocks per track according to the Table of Block Sizes). An estimated 15000 members are stored.
The library contains 30,000 physical blocks (5 blocks/track x 6000 tracks). If you omit the DATASETS=nnnnn parameter, approximately 10,000 directory entries are created (two-thirds the estimated 15,000 directory entries).
After formatting the library, PAN#4 produces a one page CA Panvalet Library Status and Activity Report. Contained in this report is the allocated storage capacity of the library.
Each time PAN#2 (PRINT command) produces a complete directory listing, this report is printed and includes the allocated storage plus actual storage in use and storage still available. So you are continually informed of the composition and growing volume of your library.
For more information about this report, see Library Status and Activity Report.