Allocating a large VLS file

Products

Ideal IPC Datacom

Issue/Introduction

When allocating and formatting a VLS file for use with Ideal or Datacom/DB, the internal addressing configuration dictates how large the VLS file can be. If the upper limit is exceeded, error messages like this from the VLSUTIL program could be received:

DISK SPACE ALLOCATION IS GREATER THAN MAXIMUM ALLOWED. EXCESS SPACE IS WASTED
RUN CANCELLED. ERROR CODE IS 0212

Environment

z/OS

IPC 15.1

Resolution

Since IPC version 14.0, a new parameter was introduced for the FORMAT function - LIBFMT= {H | F}. This parameter identifies whether the block number is stored as a 2-byte value (parameter value H for halfword), or as a 4-byte value (parameter value F for fullword). If this is not specified, blocks will use the 2-byte format. The result, as specified in the IPC Implementation Guide:

With the old 2-byte block numbering format, the maximum amount of space that can be allocated to one VLS library is 60900 blocks. With the new 4-byte block numbering format, the maximum space limitation for the VLS library is 65,535 tracks.

Here is a table showing three common blocksizes, and the maximum number of blocks or tracks that can be allocated , depending on whether LIBFMT=H, with its maximum number of blocks, or LIBFMT=F, with the maximum allocation of 65 535 tracks (4369 cylinders):

Block	Blocks	LIBFMT=H			LIBFMT=F
Size	per track	Max Trks	Max Cyls	Max blocks	Max Trks	Max Cyls	Max blocks
1960	28	2175	145	60900	65535	4369	1834980
2000	26	2342	156	60900	65535	4369	1703910
4000	12	5075	338	60900	65535	4369	786420

To allocate and initialize this VLS file, use a JCL like this below. Note that secondary allocations are not used with VLS files. Code the correct BLKSIZE and NAMELEN values for the specific VLS file.

//FMTVLS01 EXEC PGM=VLSUTIL
//         INCLUDE MEMBER=IPCSTLIB
//         INCLUDE MEMBER=IPCDDOUT
//VLSFILE  DD DSN=YOUR.VLS.LIB,DISP=(,CATLG,DELETE),
//            UNIT=3390,VOL=SER=volser,
//            DSORG=DA,SPACE=(CYL,(number))
//SYSIN    DD  *
 FORMAT BLKSIZE=4000,NAMELEN=24,LIBFMT=F
/*

Additional Information

For more information on handling VLS files, please refer to the Datacom Tools documentation section VLS Utility (VLSUTIL)