MainframeVB and VB Dump formats

Mainframe VB files

Mainframe VB files consist of a Record Dscriptor Word (rdw) followed by the lines data

  <rdw><Data Line 1             >
  <rdw><Data Line 2                     >
  <rdw><Data Line 3   >
  <rdw><Data Line 4            >

Record Descriptor Word

The record descriptor word consists of

• 2 byte Record length (including the record descriptor word). So if the record (line) is 5 bytes long this value will be
  9 (5 for the record + 4 for the rdw).
• 2 byte (value=0)

So you might have in the file

 RDW bytes   Data           
  0 19 0 0   <15 bytes record    >
  0 24 0 0   <20 bytes record         >
  0 16 0 0   <12 bytes record >

The 2 zero bytes can be used to check/comfirm it is a valid VB file.

VB Dump and VB Dump 2 formats

The VB-Dump format is the The traditional raw disk format for VB files (These day's the old Traditional mainframe disks are simulated on normal RAID systems).
The file is broken up into blocks. Each block start with a Block Descriptor Word (BDW) followed by mutiple <rdw>Records</rdw>

<BDW>
    <rdw><Data Line 1             >
    <rdw><Data Line 2                     >
    <rdw><Data Line 3   >
    <rdw><Data Line 4            >
<BDW>
    <rdw><Data Line 5             >
    <rdw><Data Line 6                     >
    <rdw><Data Line 7   >
    <rdw><Data Line 8            >

Block Descriptor Word

When the block size is < 32k, the BDW is exactly the same as the RDW
for both VB Dump and VB Dump 2 formats.
Currently when greater that 32kb:

• VB Dump is based on a definition for Tapes. I have not tested it with blocksizes > 32k
• VB Dump 2 is based on a file supplied by the user

Sample

  BDW bytes | RDW bytes | Data
  0 63 0 0
            | 0 19 0 0  | <15 bytes record    >
            | 0 24 0 0  | <20 bytes record         >
            | 0 16 0 0  | <12 bytes record >
 0 78 0 0
            | 0 19 0 0  | <20 bytes record         >
            | 0 24 0 0  | <25 bytes record              >
            | 0 16 0 0  | <17 bytes record      >

Checking

You can use the Zero-bytes in the VB / VB Dump formats to check / validate the files. You should check for VB Dump first because
a VB Dump file also looks like a VB File (with very long records).