There are three ways that IOSCDR can retrieve a CDR:
- Directly from the specified device. Specified as READ=IO, this
option is slower because it requires I/O, but it provides more current
information than READ=NOIO. This option will always give you the CDR
that the control unit is currently providing when you issue IOSCDR.
- From the system. IOSCDR retrieves the last CDR known to MVS™ for the specified
device and path. Specified as READ=NOIO, this option is quicker than
READ=I/O, but it is not as current.
- Either from the system or directly from the device, depending
upon whether the device and path are online. Specified as READ=COND,
this option allows the system to decide how to retrieve the CDR.
READ=COND returns the most accurate CDR in the shortest time possible,
because it performs no I/O if the device and path are online.