## 4.3.6 Sharing the TS7700 by multiple hosts 

Each multi-cluster grid or stand-alone grid has its own library sequence number, which is used to define the logical library to the host. Each logical library that is identified as a composite library resembles a separate library to the host. A TS7700 can be shared by multiple z/OS, VM, VSE, and TPF systems. 

Sharing can be achieved in the following ways: 

GLYPH<SM590000> By logically dividing the TS7700 into separate partitions ( partitioning ) 

GLYPH<SM590000> By enabling all attached systems to sequentially access all physical and logical volumes ( sharing ) 

Sharing an IBM system-managed library means that all attached hosts have the same access to all volumes in the tape library. To achieve this sharing, you must share the host CDSs; that is, the TMS inventory and the TCDB, among the attached hosts. 

Also, you must have the same categories that are defined in the DEVSUPxx member on all hosts. In general, these requirements can be met only in a single-platform environment. In this configuration, only one global tape volume scratch pool per media type is available. 

## 4.3.7 Partitioning the TS7700 between multiple hosts 

Partitioning is the solution if you need to dedicate the use of volume ranges to certain systems or complexes, or separate host platforms. Dividing one or more libraries into logical libraries is the easiest way to enable different hosts to access them. Each host or complex owns its own set of drives, volumes, and DEVSUPxx scratch categories that another system or complex cannot access. Each system knows only about its part of the library. Partitioning is also appropriate for the attachment to a z/OS LPAR for testing. 

This partition is implemented through values that are updated in the DEVSUPxx category definitions. Historically, you needed to change the DEVSUPxx member and IPL the system to modify a category value. Today, the use of the DS QLIB,CATS  command enables you to query and modify these category values without an initial program load (IPL). However, this command must be used with great care because a discrepancy in this area causes scratch mounts to fail. 

## Partitioning the TS7700 with Selective Device Access Control 

SDAC enables exclusive access to one or more volume serial number (VOLSER) ranges by only certain LCUs or subsystem IDs within a composite library for host-initiated mounts, ejects, and changes to attributes or categories. 

You can use SDAC to configure hard partitions at the LIBPORT-ID level for independent host LPARs or system complexes. Hard partitioning prevents a host LPAR or system complex with an independent tape management configuration from inadvertently modifying or removing data that is owned by another host. It also prevents applications and users on one system from accessing active data on volumes that are owned by another system. 

SDAC is enabled by using FC 5271, Selective Device Access Control. This feature license key must be installed on all clusters in the grid before SDAC is enabled. You can specify one or more LIBPORT-IDs per SDAC group. Each access group is given a name and assigned mutually exclusive VOLSER ranges. Use the Library Port Access Groups window on the TS7700 MI to create and configure Library Port Access Groups for use with SDAC. 

