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258 IBM System Storage DS6000 Series: Copy Services with IBM System z
Start change recording: Apply changes only from the source volume to the target
volume which occurred to the source volume in between FlashCopy establish operations
—except for the first time when FlashCopy is initially established.
Persist: Keep the FlashCopy relationship until explicitly or implicitly terminated. This
parameter is automatic due to the
nocopy property.
Nocopy: Do not start background copy from source to target, but keep the set of
FlashCopy bitmaps required for tracking the source and target volumes. These bitmaps
are established at the first time when a FlashCopy relationship is created with the nocopy
attribute. Before a track in the source volume B is modified, between Consistency Group
creations, the track is copied to the target volume C to preserve the previous point-in-time
copy. This includes updates to the corresponding bitmaps to reflect the new location of the
track that belongs to the point-in-time copy. Note that each Global Copy write to its
secondary volume within the window of two adjacent Consistency Groups may cause
FlashCopy I/O operations.
Some interfaces to trigger this particular FlashCopy relationship combine these attributes into
a single parameter such as MODE(ASYNC) with the TSO command for z/OS.
22.3.5 Define Global Mirror session
Creating a Global Mirror session does not involve any volume within the local nor the remote
sites. Our focus is back again onto the local site; see Figure 22-13.
Figure 22-13 Define Global Mirror session
Defining a Global Mirror session, creates a kind of token, which is a number between 1 and
255. This number represents the Global Mirror session.
This session number is defined at the LSS level. Each LSS that has volumes which will be
part of the session needs a corresponding define session command. Currently only a single
session is allowed per storage server. The architecture allows for more than one session and
will be exploited in the future.
Global Copy
Primary
Primary
Primary
Primary
A
B
Host
Remote site
Local site
Secondary
PENDING
FlashCopy
C
MODE(ASYNC)
Tertiary
T
B
M
S
B
M
Define Global Mirror session
01