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284 IBM System Storage DS6000 Series: Copy Services with IBM System z
commands. In our example, we assume that there is a host connection to the remote storage
disk subsystem; see Figure 23-11.
Figure 23-11 Failover from B to A
Doing a Failover (Copy Services Failover function) on the Global Copy secondary volumes
will turn them into primary volumes, and suspend the volumes immediately. This sets the
stage for change recording when application updates start changing the B volumes. Change
recording in turn allows you to just resynchronize the changes later from the B to the A
volumes, before returning to the local site to resume the application again at the local site. But
at this stage the B volumes do not contain consistent data—they are still useless. We just
changed their state from secondary copy pending to primary suspended. The A volumes
state remains unchanged.
Example 23-4 shows the establish command that we give at the secondary site. The key with
this command is the FAILOVER option. It is this option that invokes the Failover function of
Copy Services. After this action, the B volume becomes the primary volume, and the A
volume becomes the secondary, even though A may not be available and will remain as
primary full duplex.
Example 23-4 ESTPAIR command with Failover action
//* ---------------------------- TSO --------- FAILOVER (3) ------ ***
//* ESTABLISH GLOBAL COPY PAIR(S) FAILOVER PRIM(B) -> SEC(A) ***
//* ***
//* NOTE: ACTION IS NOT VALID WITH MODE(COPY) ***
//* -------------------------------------------------------------- ***
//EPAIRFO EXEC PGM=IKJEFT01
//SYSPRINT DD SYSOUT=*
//SYSTSPRT DD SYSOUT=*
//SYSTSIN DD DDNAME=SYSIN
CESTPAIR DEVN (X'3C00') +
PRIM (X'3C00' 73081 X'00' X'0C') +
SEC (X'2C00' 27131 X'00' X'0C') +
ACTION(FAILOVER) +
ONLINSEC(NO) MSGREQ(NO) CRIT(NO) +
OPTION(XD) CASCADE(NO)
FlashCopy
Primary
Primary
A
Primary
Primary
A
Tertiary
C
Primary
Primary
A
Primary
Primary
A
B
Host
Remote site
Primary
Primary
A
Primary
Primary
A
Primary
A
PENDING
Failover B to A
Primary
SUSPENDED
Local site