Setting GDPS up

The principle control member for GDPS is the GEOPARM. It contains all the disk and mirroring definitions. The location of the geoparm will be site dependent. This page shows how to define a simple geoparm to mirror between two sites, from a typical GDPS configuration from about 2006 and so will just give you a feel for what is required. You will need to consult with IBM to get up-to-date configurations.

The geoparm has four components.

  • The link definitions, starting GEOPLEX LINKS. You will change the link definitions if you add or remove LCUs, or DASD subsystems
    A typical link definition looks like
    This shows 4 links connecting 2 storage subsystems. 'SITE1' means this definition is for links going from primary to secondary. You pair this with a set of SITE2 definitions going in the opposite direction. 'B000' is the SSID of the 1st LCU on the primary box, 'E000' is the SSID of the 1st LCU on the secondary. The 'Y' means freeze is active, the 'N' means 'freeze and go' The 00050000 etc, are the PPRC link addresses, and the 'C' just means the entry is continued on the next line.
  • The disk definitions, starting GEOPLEX MIRROR. You change this if you add new disks, or if you want to make a non-mirrored device mirrored, or visa-versa.
    Typical mirror definitions look like


    The PPRCSSID statement links a primary 'controller' with its secondary, and with its FlashCopy disk (if you are using flashcopy under GDPS at the secondary site). In the example above, we have a 105 GB array being mirrored to the front half of a 210 GB array, with the back half of the array used for FlashCopy. so in the first case, we are linking controller B000 (primary) to E000 (secondary).

    Then you specify the disks in the PPRC line. PPRC='F000,B000,36,N,,B023' means F000 is the first disk on the primary, B000 is the first disk on the secondary, and we are mirroring 35 disks in that array. We don't mirror the last disk, as that is a Utility volume. The 'N' means the mirroring is not critical. B024 is the start address of the FlashCopy disks. What's confusing is that the addresses are in hex, and the counts are in decimal. So 35 is hex '22', if you start counting from hex'00'. So the secondary disks run from B000 to B023 = 36 disks, then the flashcopy disks start at B024.

    The second example above is more complex. In this case, we want to mirror the first 23 disks, miss the 24th, then mirror the rest to 36, with the corresponding disks defined for flashcopy. We need two PPRC statements to do this.
    We start mirroring B100 to B116 for 23 disks = hex'16' (counting from 0 remember), and flash from E123 to E139. Then we start the second chunk at B118, the mirrors start at E118, but the FlashCopy disks start at E13B. 3B is 36+23+1 in hex, counting from 00.

    The moral to this tale, is mirror as many of your disks as you can, and if at all possible, put the ones you don't mirror at the end of the Logical Control Unit addresses, to keep the Geoparm simple.

    The 'missing parameter' between the N,,E124 is for flashcopy disks at the primary site, if you have them installed and want them defined to GDPS.

  • The Tape definitions, starting GEOPLEX TAPEMIRROR

    The tape library is known as a Peer to Peer Virtual Tape System (PtPVTS), and consists of a pair of mirrored VTS systems. Each physical VTS has a name, and ideally should be in different sites. The example below shows a library called PTPLIB1, which consists of a pair of VTS systems called LVTS1 and RVTS1. LVTS1 is in the local site, RVTS1 is in the remote site. The 'Y' on the end of the statement indicates that freeze is enabled for this pair.


    Take a look at the GDPS and Tape section for an explanation of how GDPS freeze works with tape.

  • The utility devices, starting GEOPLEX NONSHARE.

    GDPS uses utility devices to communicate with the logical control units. They must not be mirrored. If you add a new LCU, you must define a utility device on each LCU, then add them to the GEOPARM. If possible, you want to use small hypervolumes for these.

    An example of a utility device definition is


    Nice and easy, all this means that B024 is a utility volume, and is located on logical subsystem number 00. You don't need to specify the LSS number if you have APAR OW48082 installed.

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