Any bus containing a Medium Changer device via LUN 1 of a drive is referred toas a control and data path. Any other bus is referred to as a data path. Forinformation about control paths, see “Using Multiple Control Paths” on page 3-2.Terminating the BusThe SCSI bus and all of the wires in the SCSI cable must be properly terminatedaccording to the SCSI standard.You can plug an external terminator into one of the SCSI connectors. A terminatormust be installed on the last device on each end of a string of multiple devices. Aterminator is included with each SCSI Ultrium Tape Drive.SCSI Differential - LVDLVD tape devices support a bus length of 25 meters (82 ft.) point-to-point, and 12meters (39 ft.) using multi-drop interconnection (daisy-chaining). For eachdaisy-chained device, the maximum cable length must be reduced by 0.5 meters(1.6 ft).Important: A faster bus does not imply that an attached device will support thatdata rate, but that multiple devices can operate on the bus at thatmaximum speed. For a detailed table of SCSI terms and relatedspecifications, refer to the SCSI Trade Association Web site athttp://www.scsita.org/terms/scsiterms.html. To ensure bestperformance, if possible, avoid daisy-chaining.SAS InterfaceA drive sled with a SAS (Serial Attached SCSI) interface can be linked directly tocontrollers. SAS is a performance improvement over traditional SCSI because SASenables multiple devices (up to 128) of different sizes and types to be connectedsimultaneously with thinner and longer cables; its full-duplex signal transmissionsupports up to 6.0 Gb/s. The SFF-8088 SAS connectors on the Ultrium 5 tapedrives are compatible with SAS-1 or SAS-2 cables. The SFF-8088 SAS connectors onthe Ultrium 3 and Ultrium 4 tape drives are compatible with SAS-1 cables. Inaddition, SAS drives can be hot-plugged.SAS drives will auto-negotiate speed. There are no configurable topologies thus nofeature switches associated with SAS. The SAS Ultrium 3 and Ultrium 4 half heightdrive sleds are single ported and can only be attached to one host. The Ultrium 4full height and Ultrium 5 drives are dual ported, and can be attached to amaximum of two hosts. The intention of the second port is for redundancy; forfailover rather than sharing. Sharing between these two hosts is limited toactive/passive cluster failover. LAN-free drive sharing is not supported. Ultrium 3and Ultrium 4 SAS drive sleds use the SFF-8088 connection at the drive sled endand SFF-8088 or SFF-8470 at the host adapter end. Initially, only point-to-pointconnections are supported.Fibre Channel InterfaceFibre Channel allows for an active intelligent interconnection scheme, called aFabric, to connect devices. Everything between the ports on Fibre Channel is calledthe Fabric. The Fabric is most often a switch or series of switches that takes theresponsibility for routing.The library allows the selection of the following Fibre channel port behaviors:v LN Port: (default setting) - an automatic configuration that tries arbitrated loopfirst, then switched fabricChapter 3. Installation Planning 3-9
