Configuration of the recovery site

The hardware configuration can be different at the recovery site, as long as it supports data sharing.

The recovery site must have a data sharing group that is identical to the group at the local site. It must have the same name, the same number of members, and the members must have the same names as those at the local site. The CFRM policies at the recovery site must define the coupling facility structures with the same names as those at the local site (although the sizes can be different).

You can run the data sharing group on as few or as many z/OS® systems as you want.

Conceptually, there are two ways to run the data sharing group at the recovery site. Each way has different advantages that can influence your choice:
  • Run a multi-system data sharing group.

    The local site is most likely configured this way. You have a Parallel Sysplex® containing many CPCs, z/OS systems, and Db2 subsystems. This configuration requires a coupling facility, the requisite coupling facility channels, and the Sysplex Timer.

    Using a multi-system data sharing group at the recovery site, you have the same availability and growth options that you have at the local site.

  • Run a single-system data sharing group.

    In this configuration, you centralize all of your Db2 processing within a single, large processor, such as an IBM® System z114 or z196 or subsequent 64-bit z/Architecture® processor. As the following figure shows, you must install a multi-member data sharing group. After the group starts up, you shut down all but one of the members and access data through the remaining member.

    Figure 1. Example of local and disaster recovery site configurations. With this configuration, the recovery site can be a single-system data sharing group. After the data sharing group is started on the recovery site, you can stop all but one of the members.
    Begin figure summary.The local site runs with two Sysplex timers while the single-system disaster recovery site runs with a processor clock (TOD clock). Detailed description available.
    With a single-system data sharing group, you lose the availability benefits of the Parallel Sysplex, but the group has fewer hardware requirements:
    • The Sysplex Timer is not needed; you can use the CPC's time-of-day clock.
    • You can use any available coupling facility configuration for the recovery site system, including Integrated Coupling Facilities (ICFs).
      With a single-system data sharing group, there is no longer inter-Db2 read/write interest, and the requirements for the coupling facility are as follows:
      • A lock structure (which can be smaller)
      • An SCA
    Group buffer pools are not needed for running a single-system data sharing group. However, you do need to have at least small group buffer pools for the initial startup of the group. Db2 allocates them and uses them to do its damage assessment processing. When you are ready to do single-system data sharing, you can remove the group buffer pools by stopping all members and then restarting the member that is handling the workload at the disaster recovery site.