Optical media

 

Optical media library devices allow you to archive information to optical media, and they provide backup and recovery capability similar to tape media.

Characteristic Comparison
Access to data Optical devices are random access devices. File access is independent to the order in which the data is stored. Multiple users can access the same volume simultaneously.
Data transfer rates Data transfer rates for tape tend to be higher than for optical, particularly if you use tape drive compression.
Durability Optical media has a life span around 50 years.
Archiving Write Once Read Many (WORM) optical media is made for archiving. Each sector on the media can only be written to once, when creating and updating files and directories. When a file is changed or deleted, a new version of the file gets written, and the old version still exists on the media. This unique characteristic of never rewriting the same sector is that it allows all previous versions of every file to remain on the media.
Transportability DVD-RAM media created or written to on the system can be read from any platform that supports the Universal Disk Format (UDF) file system. UDF is an industry standard file system.

 

How random storage mode affects save functions

Optical devices use a random storage mode to save information. Optical devices use a hierarchical file structure when the system accesses files on the media.

You may specify a path name for the optical file in the save operation beginning with the root directory. If you specify an asterisk (*), the system generates an optical file name in the root directory (/). If you specify an 'optical_directory_path_name/*', the system generates an optical file name in the specified directory on the optical volume. If the directory does not exist, the system creates the directory.

For example, if you specify SAVLIB LIB(MYLIB) DEV(OPT01) OPTFILE('MYDIR/*'), the system creates the following optical file: MYDIR/MYLIB.

The system looks for active files on the optical media volume for the same file that you save currently. For example, you previously saved a SAVLIB to optical media. Now you run a new SAV command to the same media; the system ignores the SAVLIB files and does not report any active files for your SAV command.

In general, the save operation looks for an active file that matches the pathname specified on the OPTFILE parameter. SAVSYS and options 21 and 22 of the SAVE menu look for any active file.

Table 2. Checking for active files on optical media
Consideration General information
CLEAR(*NONE) parameter

If you specify CLEAR(*NONE) on the save command, the system checks the optical media volume for active optical files. The system looks for active files with the same name and path as the specified optical file.

If the system finds an optical file that is identical to the specified optical file, the system displays an inquiry message. You may respond to the message by cancelling the process, writing over the existing file on the volume, or inserting a new cartridge.

If the system does not find any active files and there is enough space on the optical volume, the system writes the files to the media. If the system does not find enough available space on the optical media volume, the system prompts you to insert a new media volume in the media device.

CLEAR(*ALL) parameter

The CLEAR(*ALL) parameter automatically clears all of the files on the optical media volume without prompting.

CLEAR(*AFTER) parameter

The CLEAR(*AFTER) parameter clears all the media volumes after the first volume. If the system encounters the specified optical file on the first volume, the system sends an inquiry message that allows you to either end the save operation or replace the file.

CLEAR(*REPLACE) parameter

The CLEAR(*REPLACE) parameter automatically replaces active data of the specified optical file on the media volumes.

Check for active files parameter on the GO SAVE command

During a GO SAVE command, menu option 21 or 22, or a SAVSYS command if the system detects an active file of the specified optical file, it displays message OPT1563 in the QSYSOPR message queue. During other save command operations, the system may display message OPT1260 depending on the value of the CLEAR parameter. If the system does not detect an active file of the specified optical file, the system checks for available space. If there is room to write the file, the system writes the file to the current volume in random mode. If there is not enough room, the system prompts you to insert another optical media volume into your optical device.

During a GO SAVE command, menu option 21, you specify Y or N at the Check for active files prompt to see if there are active files on your media volume.

  • Check for active files: N option

    When you select the Check for active files: N option, the option forces the system to automatically overwrite all files on your DVD-RAM optical media.

  • Check for active files: Y option

    When you select the Check for active files: Y option, the option forces the system to check for active files on your DVD-RAM optical media.

SAVSYS command messages

When you run a SAVSYS command to an optical media volume, the system displays message OPT1503 - Optical volume contains active files if there are active files on the optical media volume. You can either initialize the media with the Initialize Optical (INZOPT) command or you can specify CLEAR(*ALL) on the SAVSYS command to run an unattended save.

 

Parent topic:

Choosing your save media
Related reference
Choosing your save media
Related information
Comparison of offline storage
Optical storage