Linking and Sharing Minidisks

If your files are stored on minidisks, you will need to link to other users' minidisks in order to share files. This section contains the information you will need in order to create temporary or permanent links to other minidisks.

Since only one user can own a minidisk, and there are many occasions that require users to share data or programs, z/VM® lets you share minidisks, on either a permanent or temporary basis, by linking.

Virtual disks in storage that are defined in the directory, although they are temporary, can be shared among users. A shareable virtual disk in storage exists from when the first user links to it until the last user detaches it or logs off. Because of its temporary nature, however, a shareable virtual disk in storage should not be used for permanent data.

Permanent links can be established for you in your z/VM directory entry. These minidisks are then a part of your virtual machine configuration every time you log on. You can also have another user's minidisk temporarily added to your configuration by using the CP LINK command.

Coding in the file of access For example, if you have a program that uses data that resides on a minidisk identified in the user ID INFO's configuration as 194, and you know that the password assigned to this minidisk is GO, you could enter the command:
link info 194 as 198 r pass= go
The r in the command indicates the access mode; in this case, it tells CP that you only want to read files from this minidisk and you will not write to it. If you try to enter this command when someone already has write access to that minidisk, you will not be able to establish the link. If you want to link to INFO in any event, you can reenter the LINK command using the access mode RR:
link info 194 198 rr go
Notes:
  • Using the RR access lets one user read a minidisk while another is updating it at the same time. This can produce unpredictable results.
  • The password cannot be entered on the command line if the password suppression facility is active.
  • If RACF® or another external security manager is installed on your system and is in effect, the procedure for linking may be changed somewhat. For more information, see your system administrator.

Once successfully completed, INFO's 194 minidisk is then added to your virtual machine configuration at virtual device number 198.

To verify the command has been processed, you can enter the CP QUERY DASD command, which will result in a display similar to this:
DASD 191 3390 USG017 R/W     20 CYL  ON DASD  0541 SUBCHANNEL = 0003
DASD 198 3390 USG01M R/O    120 CYL  ON DASD  0565 SUBCHANNEL = 0001
You can also use the CP LINK command to link to your own minidisks. For example, if you log on and discover that another user has access to one of your minidisks, you will be given read-only access, even if it is a read/write minidisk. You can request the other user to detach your minidisk from his virtual machine, and after he has done so, you can establish the link:
link * 191 191
When you link to your own minidisks, you can specify the user ID as *, and you do not need to specify the access mode or a password.

For complete information and options available for the CP LINK command, see z/VM: CP Commands and Utilities Reference.