Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

2-18 About TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
R-VOL Read Option
For additional flexibility, TrueCopy for z/OS offers a special R-VOL read option.
The Hitachi representative enables the R-VOL read option on the RCU (mode
20). The R-VOL read option allows you to read a TCz R-VOL only while the pair
is suspended, that is, without having to release the pair.
Note: When you read a TCz R-VOL from a host, the reference date in the
VTOC is updated. In this case, you must permit to update the VTOC.
The RCU will allow you to change only the VOLSER of the suspended R-VOL, so
that the R-VOL can be online to the same host as the M-VOL while the pair is
suspended. All other write I/Os will be rejected by the RCU. The MCU
copies the M-VOL VOLSER back onto the R-VOL when the pair is
resynchronized.
If mode 20 and mode 190 is enabled simultaneously, the Hitachi
representative permits to only update the VOLSER and VTOC of the TCz R-VOL
from a host while a pair is suspended. The MCU copies the M-VOL VOLSER and
VTOC back onto the R-VOL when the pair is resynchronized.
When the R-VOL read option is not enabled and/or the pair is not suspended,
the RCU rejects all read and write I/Os to a TCz R-VOL. Note: If you need
write access to an R-VOL, you must release the pair.
Note: For 2105 or 2107 controller emulation, the CSUSPEND command to the
R-VOL of a suspended TCz pair will be rejected when the TCz R-VOL read
option is used.