The purpose of TCR is to provide a way to reliably recycle fragmented tapes that will guarantee a certain number of input tapes will be returned to scratch for each scratch tape used for output. If the requested ratio of returned tapes cannot be achieved, the RECYCLE command is not performed.
When a RECYCLE GROUP command is coded with a TARGET parameter that does not include the tape type defined by the SOURCE parameter the TCR value is automatically set to zero. TCR is set to zero because the ratio is calculated based on the SOURCE tape type defined, but the SOURCE tapes will not be the tapes released by the RECYCLE command. For example, RECYCLE GROUP(nn),SOURCE(PRIMARY),TARGET(DUPLEX). This command will cause PRIMARY tapes to be read to create new DUPLEX tapes. If TCR was added to this command, the ratio calculated would be based on the PRIMARY tapes, but it is the DUPLEX tapes that will be released. No PRIMARY tapes will be released or recataloged. In this situation there is no way to guarantee that the calculated ratio will actually be achieved so the TCR value coded will be automatically changed to zero, a warning message will be issued and the RECYCLE GROUP command will be processed with a TCR of 0.
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