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 |
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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.
