>Well, there seems to be some disagreement here. And some misunderstanding as well. When Jim talks about multiple paths for the I/O, it is multiple paths to the control unit (that has a bunch of devices). So you can have multiple I/O's active at the same time to different devices on the same control unit. The operating system can get this without knowing much about it.
The other issue is whether you can have multiple I/O's at the same time to the *same* device (when the read could be satisfied from CU cache while you wait on the write to complete). Provided the channel program clearly indicates its intentions you could, but I understand you need PAV. VM itself does not support PAV, but I think you can allow the guest to do so on dedicated DASD devices, right? I have no idea what the Linux kernel config option does, and I trust Carsten if he says it does not do it for us. Rob
