Storage Device Operation Overlap in Multiple Device Subsystems
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2005-Feb-19
In tape storage subsystems that include a control unit and multiple storage devices, it can be advantageous to have an overlapping of tape motion operations. Where devices with slower access times are being used, the performance penalty is high if conventional methods are used to read or write data when multiple devices are required. In that case, data on one device must be completely read back and verified by the control unit (C.U.) before it is free to send a read or write command to another device. However, if access/start times are known, it is possible to issue start commands to the next required device in the subsystem while still processing data on the present device. In addition, where a device uses different home or stop-lock positions for write or read, repositioning could also be accomplished in the overlap mode.