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46 IBM System Storage DS6000 Series: Copy Services with IBM System z
While the FlashCopy relationship is being created, the DS6000 holds off the I/O activity to
the volume for an interval of time by putting the source volume in an
extended long busy
condition. No user intervention is required. I/O activity resumes when the FlashCopy
establish process is completed.
If all bits for the bitmap representing the target are set to their initial values, this means
that no data block has been copied so far. The data in the target is not modified during
setup of the bitmaps. At this very first step the bitmap and the data look as illustrated in
Figure 6-2.
Figure 6-2 FlashCopy at time t0
Once the relationship has been established, it is possible to perform read and write I/Os
on both the source and the target. Assuming that the target is used for reads only while
production is ongoing, things will look as illustrated in Figure 6-3.
Figure 6-3 Reads from source and target volume and writes to source volume
1 1 1 111
bitmap
t t t ttt
source
data
000
target
data
0
0
0
time
t
0
FlashCopy established at time t0 (time-zero)
time
Writing to the source and
reading from the source and the target
t
0
1 0 1 110
bitmap
t t t ttt
data
00z
t t
target
data
x
0
00
0
write x write y
t
x
t
y
read
read 1
read 2
before physical write to the source:
copy time-zero data from the source to the target
time-zero data not yet
available in the target:
read it from the source.
source
write z
t
z