Figure 13-11 shows the TS3500 tape library Shuttle System Architecture with four logical  libraries. The HPSS SCSI physical volume repository (PVR) controls a library string of up to eight  logical libraries. The HPSS SCSI PVR has at least one connection to, and knowledge of, the  contents of each logical library in its configuration. Furthermore, the SCSI PVR is aware of  the basic connectivity between logical libraries (HPSS requires all logical libraries to have a  direct connection) through the Shuttle Call System (SCS) component, which is an API for  managing and controlling shuttle connections.  When movement across the shuttle is necessary, the HPSS SCSI PVR also can use the SCS  component to make an exclusive connection between two shuttle-connected libraries that are  available for the move. After it is completed, the SCSI PVR can use SCS to release this  exclusive connection and that shuttle connection can serve other requests. To move a cartridge from one library string to another, the cartridge is first placed in a shuttle  car by the cartridge accessor. The cartridge is then moved across the shuttle connection and  is removed by the cartridge accessor at the destination library. The time for the shuttle car to  move from one library to the next varies based on installation distances, but is as low as  5 seconds in optimal configurations. Mount performance and cartridge move time in a shuttle complex depends on the overall  configuration of the complex, including the length of the shuttle connections and the location  of the available drive. To maximize performance, the application should use only remote tape  drives if all drives are full in the home logical library. 372  IBM Tape Library Guide for Open Systems Performance considerations HPSS SCSI PVR interface to the Shuttle Call System Figure 13-11 TS3500 tape library shuttle system architecture Library management (LM) software for Logical Complex A (e.g. HPSS PVR) Shuttle Call System (SCS) Device Driver Data movement software for Logical Complex A (e.g. HPSS Data Movers) Device Driver LAN SAN Control Paths Data Paths (SAN or direct-attach) Logical Library (LL1A) Logical Library (LL2A) Logical Library (LL3A) Logical Library (LL4A) Shuttle connection Shuttle connection Admin and Service LANs TS3500 Admin (GUI/CLI) TS3500 Service (TSSC) Library String 1 Library String 4 TS3500 Shuttle System Architecture