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MPE/iX File System

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The MPE/iX file system is record oriented. Each file has a file limit (DISC parameter in BUILD) which determines the maximum number of records the file can hold. Each record has a maximum record size which indicates the maximum number of bytes each record can hold. In addition, a file may have fixed or variable length records.

Typically, variable length records are more efficiently stored on the system, and less efficiently accessed. For fixed length record files, storage on the system is less efficient because of byte padding, and access is faster because the records are all the same size.

Fixed Record File Padding

Files created on MPE/iX with fixed records may result in the padding of the records to the record size specified. ASCII files are padded with blank spaces, and binary files are padded with zeros.

For example, a file named vfile containing variable length records is transferred to an MPE/iX file as follows: 

  ftp> ascii
  ftp> get vfile fixfile
The default file building parameters for ASCII transfers is fixed records of 80 bytes in length. The resulting file will be stored with 80 byte records. Records from vfile that contain fewer bytes of data will be padded with spaces.

Record Truncation

Record truncation can occur when performing a data transfer to an ASCII file on the MPE/iX system. This occurs when the number of bytes in the data transfer exceeds the maximum record size bytes in the target file. When this occurs, the target record is filled to the maximum record size bytes from the data transfer, and the remaining bytes for the current record are discarded. A warning message is displayed when this occurs.

For example, a file named zfile containing 132 byte records is transferred to MPE/iX as follows: 

  ftp> ascii
  ftp> get zfile mpefile
  Some records were truncated during transfer. (FTPWARN 15)
The default ASCII file building parameters are fixed, 80 byte records. Since the original record size is 132 bytes, only the first 80 bytes of each record are transferred, and the remaining bytes in each record are discarded.

End-of-File Limitation

When you transfer a file to an MPE/iX system using FTP, it is important to define enough MPE/iX file records for the resulting MPE/iX file. If you do not use BUILD parameters, the default maximum number of records for both ASCII and binary transfers is 204,800 records. If you are transferring a file that exceeds this default, use the BUILD parameter DISC=numrec to increase the number of records in the target file.

Be careful if you use BUILD parameters. If you do not explicitly specify the DISC=numrec parameter, the default of 1,023 records is used and may not be sufficient.

If the number of records in the target MPE/iX file is insufficient, the target file is not saved, and the existing file (if any) is preserved. An error message is displayed if this occurs.



Using BUILD Parameters with FTP

File Transfer Examples