z/OS I/O definitions
This section defines the I/O of the z/OS® operating system used by the System z® host attached to the TS7700.
Subsystem identification
Each logical controller, or 16-device group, must present a unique subsystem identification to the System z host. This ID is a 1-byte field that uniquely identifies each device associated with the logical controller within the larger storage controller. The value of this ID cannot be 0. The subsystem ID must match the LIBPORT-ID defined in the host Hardware Configuration Definition (HCD).Table 1 shows required definitions of subsystem IDs.
| Distributed Library | Logical CU | Subsystem ID/LIBPORT-ID† |
|---|---|---|
| 0 | 0-F | 0×01-0×10 |
| 1 | 0-F | 0×41-0×50‡ |
| 2 | 0-F | 0×81-0×90‡ |
| 3 | 0-F | 0×C1-0×D0‡ |
| 4 | 0-F | 0×21-0×30‡ |
| 5 | 0-F | 0×61-0×70‡ |
| 6 | 0-F | 0×A1-0×B0‡ |
| 7 | 0-F | 0×E1-0×F0‡ |
†Identical to configured LIBPORT-ID ‡Every logical controller image represents 16 tape device images and must have a unique LIBPORT-ID. The system has reserved ranges of LIBPORT-IDs to account for future node expansions at each distributed library. |
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Cluster and grid reporting
Every virtual device that is attached to a System z host and the TS7700 must report the same library sequence number that is known as the composite library ID. This is true whether the grid configuration is distributed across multiple sites, or consists of a single site. The composite library ID allows the host to consider the grid configuration as a single library.Each cluster in a grid configuration possesses a unique library sequence number that is known as the distributed library ID, that identifies it among the clusters in its grid. A distributed library ID is given to a cluster during the teach of the integrated Library Manager for the TS7700 partition. This ID is reported to the System z host upon request and is used to distinguish one cluster from another in a grid.
Host console request facility
The TS7700 permits you to make problem determinations from the System z host console by using the host console request (HCR) facility, or MVS™ Library Request (LI REQ) command. This facility performs similarly to existing library query commands; it permits an operator to request TS7700 operational information or take a limited set of actions.For example, you can use this command to request information about the following:
- The current state of grid links and copy activity between clusters
- The current state of the cache and the data managed within it associated with the specified distributed library
- The status and attributes of virtual volumes
- Usage of physical volumes and their relationships with distributed libraries
- Media types and counts for volume pools
- The content of the recall queue starting with a specified virtual volume
- Define settings for thresholds and priorities for various resources
- Define settings that control how the TS7700 manages data movement
- Promote a volume in the recall queue
- Enable or disable copies to and from a specified distributed library by using the host copy enable function
- Control deferred copy throttling
You can use HCR to temporarily override a virtual volume's assigned disk cache preference group while the volume resides in disk cache. This function can also be used to update the last recently used position of the volume as if the volume had just been mounted. If you intend to access the volume again soon, you can use this function to retain the volume in cache for a longer period. Or, you can use this function to request that the volume be migrated from cache sooner.
For a full description of how the HCR facility can be used, and for additional information regarding the MVS Library Request command syntax, refer to the white paper: IBM® TS7700 Series z/OS Host Command Line Request User's Guide at the Techdocs Library link in the Related information section.
