Rotation order

You control the rotation order to a device with the order of the:

Control unit numbers of the control units that attach to the device
Channel paths used by the control units
Note: See CNTLUNIT for a description of the CUNUMBR and PATH keywords in the CNTLUNIT statement.

Rotation order does not apply to devices assigned to CFS, CFP, CBS, CBP, ICP, CIB, CL5, CL6, or CS5 channel paths. The CSS selects the channel path that is likely to have the best response time.

The rotation order for a control unit header is built using the first channel path you specify for each control unit that attaches to a device, beginning with the lowest numbered control unit. The rotation order then is built using the second channel path, if any, for each control unit beginning with the lowest numbered control unit. The rotation order is built by repeating this procedure until all channel paths for all the control units contained in a control unit header have been added.

Control Unit Header 2 in Figure 1 shows an example of how specifying paths in a control unit header can affect the path rotation order. If you specify PATH=(01,07) in the CNTLUNIT statement for physical control unit 2 and PATH=(02,04) for physical control unit 3, the rotation order for device B is 01, 02, 07, 04. However, if you specify PATH=(07,01) in the CNTLUNIT statement for control unit 2 and PATH=(02,04) for control unit 3, the rotation order for device B is 07, 02, 01, 04.