Concepts for virtual storage

This topic provides general information about virtual storage, including descriptions and instructions for use.

When you use virtual storage, you create virtual tape, CD, or DVD images that exist on your server disk units. The objects that virtual storage uses are as follows:

Virtual storage device

A virtual storage device is a device description that supports virtual storage, like an actual tape or optical device description supports actual storage. One to 35 virtual storage tape device descriptions and one to 35 virtual storage optical device descriptions can be active at a time on the server.

You create a virtual tape device by selecting the RSRCNAME(*VRT) or TYPE(63B0) parameters on the Create Device Description (Tape) or (CRTDEVTAP) command.

You create a virtual optical device by selecting the RSRCNAME(*VRT) or TYPE(632B) parameters in Create Device Description (Optical) or (CRTDEVOPT) command.

Image catalog

An image catalog is an object that can contain up to 256 image catalog entries. Each catalog is associated with one user-specified integrated file system directory. The system-recognized identifier for the object type is *IMGCLG. Image catalogs can have the following statuses:

Ready: All of the loaded and mounted image catalog entries are available for use by the virtual storage device. The image catalog can be made ready by using the LODIMGCLG (Load Image Catalog) command with the parameter OPTION(*LOAD).
Not Ready: None of the image catalog entries in the image catalog are available for use by the virtual storage device.

You can view or change image catalogs by using the Work with Image Catalogs (WRKIMGCLG) command.

Write protection

Write protection refers to whether you have enabled the write protection switch for an image catalog entry. The status for write protection are as follows:

Y: Write protection is set for the image catalog entry. You cannot write to the virtual image associated with the image catalog entry.
N: Write protection is not set for the image catalog entry. You can write to the virtual image associated with the image catalog entry.

For optical use only

Note: If the access for an optical image catalog entry is *READWRITE, you set the write protection switch to Y or N. If the access for the optical image catalog entry is *READONLY, the write protection switch is always set to Y.

You can view or change image catalog entries by using the Work with Image Catalog Entries (WRKIMGCLGE) command. The WRKIMGCLGE command indicates if the image catalog is in a Ready state or a Not ready state, and you can use this command to change image catalog entries whether the image catalog is in a Ready state or a Not ready state.

You can change image catalog entries by using the Load/Unload/Mount IMGCLG Entry (LODIMGCLGE) command or by typing GO IMGCLG at a command line.

Virtual image

A virtual image is an object that contains the data that is typically on physical media. The virtual image is a stream file that resides in the integrated file system. In a backup and recovery scenario, you can also span virtual images.