General overview for establishing ESCON paths

Figure 1 shows an example of two separate storage subsystems. In this example, device number 142 is the source volume (the volume that you plan to copy) and becomes the primary volume in the PPRC duplex volume pair. With respect to primary volume 142, the primary system consists of the host processor with ESCON® channels, the ESCON Director (ESCD), and Storage Control A. Target volume 262 (the volume to contain the copy) resides on Storage Control B, and becomes the secondary volume in the duplex volume pair. Storage Control B, which may be in the same building or may be many kilometers away, is therefore part of the recovery system for this volume pair.

This installation has established a connection from the host to the primary volume through ESCD ports A6 and A5, and a host-to-secondary connection through ESCD ports A6 and B0.

Figure 1. Storage subsystems for primary and secondary volumes

Storage subsystem connections for primary and secondary volumes

Figure 2 shows a PPRC link established between (primary) storage control A and (recovery) storage control B. The CESTPATH command ‘LINK(aaaabbcc)’ parameter to establish this link would be LINK(0000B000), where the following terms apply:

  aaaa = primary volume’s storage control cluster 0, interface A
    bb = the link destination address, ESCD port B0
    cc = For those storage controls supporting logical subsystems, this value 
         is the logical subsystem number. For those storage controls not 
         supporting logical subsystems, and for FB LSS, this value is 00.

Note:

For storage subsystems that support LCUs, see the documentation for that storage subsystem.
Before you issue the CESTPATH command, you may want to issue a CQUERY command to a device within each storage subsystem to determine the SSID and the serial number. The CESTPATH command requires this information. You can address the CQUERY command to either a simplex device or a duplex device.
You can collect path information with ICKDSF (release 17 or above) using the ANALYZE command, specifying the NOSCAN and NODRIVE keywords. Refer to Device Support Facilities (ICKDSF) User's Guide and Reference for more information.

The CESTPATH command for the example in Figure 2, using primary volume 0142, is:

     CESTPATH DEVN(X'0142') PRIM(X'6060' 62019) SEC(X'6061' 68006)
              LINK(X'0000B000')

Figure 2. Establishing a PPRC path through an ESCD

Note: The CESTPATH establishes the PPRC link, only. You must also previously configure the ESCD to establish the logical system connection between ports A5 and B0.

You do not need to go through an ESCON Director to establish a PPRC link. Figure 3 shows an example of a direct link between storage subsystem A and storage subsystem B. The installation has installed an ESCON fiber optic cable between them.

Figure 3. Establishing a direct PPRC path

The ‘LINK(aaaabbcc)’ parameter of the CESTPATH command for this example would be LINK(00150000), where the following terms apply:

         aaaa = primary volume’s storage control cluster 1, interface F
           bb = 00, as this is a direct connection
           cc = For those storage controls supporting logical subsystems, this value 
                is the logical subsystem number. For those storage controls not 
                supporting logical subsystems, and for FB LSS, this value is 00.

Note:

For storage subsystems that support LCUs, see the documentation for that storage subsystem.
More information on the CESTPATH command LINK parameter can be found CESTPATH – establishing paths.

The CESTPATH command for the example in Figure 3, using primary volume 0142, is:

     CESTPATH DEVN(X'0142') PRIM(X'6060' 62019) SEC(X'6061' 68006)
              LINK(X'00150000')

Example: The following example adds four ESCON paths between the primary site storage control (SSID 6060, serial number ending with 62019) and the recovery site storage control (SSID 6061, serial number ending with 68006). Issue the CESTPATH command to any device on the primary site storage control.

     CESTPATH DEVN(X'0142') PRIM(X'6060' 62019) SEC(X'6061' 68006)
              LINK(X'0000B000' X'0001B100' X'0016B200' X'0017B300')

Note: The above example assumes that all of the physical and logical paths already exist.