Data File Volumes
Definition
When extracting data, the system may create one or more sequential files to store the extracted data. If you specify a maximum file size smaller than the size that can accommodate the extracted data, then the system creates multiple physical files.
The physical files created for an extraction can be stored in the same directory, or they can be stored in different directories. A file volume defines the location of a single physical file.
Structure
If the data extracted fits into a single physical file, then the system creates a single sequential file and assigns it to a single volume. This volume is considered Volume 0 (zero). For example, if the user specifies DATA1998.TXT as the file name for the extract, the system creates DATA1998.TXT and assigns it to volume 0.
If the data extracted is too large to fit into a single sequential file, then the system creates several physical sequential files. The system assigns these files to volumes in the following manner: the first file created for the extract is assigned to Volume 0, the second file is assigned to Volume 1, and so on.
The following table reiterates the assignment of files to volumes:
Volume ID |
Identifies the… |
|---|---|
0 (zero) |
First file created by the extract |
1 |
Second file created by the extract |
2 |
Next file created by the extract |
… |
… |
Directory File
The system also creates a directory file containing the list of all the files that belong to the extract. This file is created even when only one sequential file is created for the extract.
The directory file resides in the same directory as Volume 0. Its name is the same as the name of Volume 0, with the suffix _DR.
Caution
Do not delete the directory file at the operating system level. If you wish to delete the files of an extract, do so from the DART utility for deleting an extract .
Physical File Names of the Volumes
Starting with the second volume, the data extract files names are a combination of the file name specified by the user and a three-character suffix indicating the volume number. The format of the suffix is: _## where ## is the volume number. For example, the suffix for Volume 1 is _01.
The following table shows an example of the physical files names resulting from an extract for which the user specified DATA1998.TXT as the file name:
Volume ID |
Identifies the File… |
|---|---|
0 (zero) |
DATA1998.TXT |
1 |
DATA1998.TXT_01 |
2 |
DATA1998.TXT_02 |
… |
… |
(Directory file) |
DATA1998.TXT_DR |
Exception to File Naming: ISO 9660 Compliant File Names
If you require ISO 9660 compliant file names (for storing files on a CD-ROM), then the physical file name is limited to eight characters for the file name and three characters for an extension (called "file type" in some operating systems).
The eight characters limit includes the three characters needed for the DART volume ID (for example, _02). This leaves only five characters for the user-specified portion of the file name.
For example, if the user specifies DATA1.TXT for file name, then the actual file names are as follows:
Volume ID |
Identifies the File… |
|---|---|
0 (zero) |
DATA1.TXT |
1 |
DATA1_01.TXT |
2 |
DATA1_02.TXT |
… |
… |
(Directory file) |
DATA1_DR.TXT |
ISO 9660 compliant file naming also requires the name to be all uppercase characters.
Use
You must define at least one Volume 0 to accommodate a single sequential file.
You must define enough volumes to accommodate the largest possible data extract. The maximum file size you set (through the
Display settings for data extraction
screen) determines how many physical files are created for any given data extract size. The smaller the maximum size is, the more files are created for a given data extract.
Integration
You configure file volumes and assign the volumes to a directory set at the same time.
You configure data volumes and directory sets through Data file configuration .