HP 3000 Manuals HP 3000 Manuals
MPE/iX File System
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 zeroes.
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.