Automated storage library having redundant scsi bus system

Abstract

An optical disk library having a redundant SCSI bus system which utilizes double-sided, multi-ported switches for connecting each of two library controllers to all library pickers and some or all of the optical disk drives in the library is disclosed. The use of additional library controllers and pickers allows for greater subsystem flexibility and redundancy. The switches minimize the need for additional SCSI adapters to the library controllers and include anti-latch circuitry between sets of transceivers to eliminate the need to know the direction of data flow on a bus. In addition, the switches are physically located apart from the SCSI adapters, pickers, and optical disk drives, thereby minimizing the amount of customization required, and permit switching from the primary library controller to the secondary library controller to provide access to any optical disk in the library when a failure in the system has otherwise made such optical disk inaccessible through the primary library controller. The pickers and optical disk drives are coupled to the switches in one or more singleended strings to simplify library operations and minimize the amount of the library made inoperative by a device failure. Each picker is coupled to the switches on a single-ended string to which no optical disk drive is attached, further reducing the likelihood that access to optical disks in the library will be lost during a failure.