Geographically dispersed parallel sysplex support for peer-to-peer VTS

The Geographically Dispersed Parallel Sysplex™ (GDPS®) integrates Parallel Sysplex® technology and remote copy technology to enhance application availability and improve disaster recovery. GDPS topology is a Parallel Sysplex cluster distributed across two sites, with all critical data mirrored between the sites. GDPS manages the remote copy configuration and storage systems, automates Parallel Sysplex operational tasks, and automates failure recovery from a single point of control, thereby improving application availability. GDPS supports all transaction managers (for example, Customer Information Control System [CICS] and Information Management System [IMS]) and data base managers (for example, DB2®, IMS™, and Virtual Storage Access Method [VSAM]).

The Peer-to-Peer VTS allows GDPS to include tape data in its management of data consistency and integrity across sites. A new I/O VTS selection option is provided for use with GDPS such that all virtual volumes are processed from a primary VTS and a copy is stored on the secondary VTS. GDPS has the control capability to "freeze" copy operations so that tape data consistency can be maintained across GDPS-managed sites. Additionally, GDPS can switch the primary and secondary VTSs, and synchronize system data sets such as catalogs, TCDB, and tape management databases with the Peer-to-Peer VTS after an emergency switchover.

The physical topology of a GDPS consists of a base or Parallel Sysplex cluster spread across two sites, with one or more z/OS systems at each site. GDPS uses the Parallel Sysplex cluster facilities to communicate between the systems. Each GDPS system joins the GDPS Parallel Sysplex cluster group. When a system joins a Parallel Sysplex cluster, GDPS automation will transfer GDPS policy and all GDPS status to the joining system.

If your installation is running Peer-to-Peer VTS under GDPS, take into account the considerations that are shown in Table 1 for your particular environment:

Table 1. Environmental considerations for a peer-to-peer VTS running under GDPS
Environment	Results	Notes
Peer-to-Peer VTS runs in immediate copy mode and is fully operational.	The host control data sets for OAM and for your tape management software are consistent with the data on your logical volumes site-to-site as long as the volumes are copied.	The Peer-to-Peer VTS library under GDPS does not support logical software partitioning.
A disaster occurs and you are running in immediate copy mode.	There is no synchronization for open logical volumes. A rerun of the workload will inform you that you have no valid copy of the data.	The Peer-to-Peer VTS library under GDPS does not support logical software partitioning.
A disaster takes place and you are in deferred mode. The distributed library that remains is the input/output (I/O) VTS for that volume.	There is no synchronization for closed and open logical volumes. Open logical volumes at the time of the disaster become invalid. Closed logical volumes at the time of the disaster are valid.	You are not able to have full control of the selection of the I/O VTS. The Peer-to-Peer VTS library under GDPS does not support logical software partitioning.
A disaster takes place and you are in deferred mode. The distributed library that is damaged is the I/O VTS for that volume. The copy process for a logical volume has not been completed.	There is no synchronization for closed and open logical volumes. Open logical volumes at the time of the disaster become invalid. Closed logical volumes on the damaged VTS at the time of the disaster become invalid.	You are not able to have full control of the selection of the I/O VTS. The Peer-to-Peer VTS library under GDPS does not support logical software partitioning.

Related reading: For more information on GDPS, see the following documents:

GDPS/PPRC Installation and Customization Guide
IBM TotalStorage™ Peer-to-Peer Virtual Tape Server Planning and Implementation Guide