>If an IO is executed in VM, is it always on the same channel? >Does DDR read the label and then write on the same channel?
Each I/O can go on a different path. A start subchannel instruction just specifies the subchannel (which maps to the device), and in no way specifies the channel path. While it is possible to control the channel paths used for I/O by manipulating the channel path masks (see the Principles of Operation), the operating system normally does not do this -- instead it lets the I/O subsystem choose the path. You get best performance that way. Path masks are only changed when you vary paths on or offline, or errors are encountered. The I/O subsystem, in turn, gets its information about what is out there from your IOCDS, so I'm not sure it can even detect the problem. But that's hardware and I only do software! The only way VM could be at fault is if the I/O subsystem presented VM with error information and VM ignored it. I'd expect that error information to be recorded in EREP, even if VM could not interpret it. Did you check the EREP?
