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Chapter 3 Notes
72
Table 3-2 Copy Control States
Copy Control State Sub-State Copy State
Sync Mode
• Updates MV and RV synchronously. After completing the MV
and RV update, informs the host of I/O completion.
• For DDR, copy is done only to the cache. Therefore, this copy
mode little lowers the performance.
• For RDR, performance lowered by this copy mode is in
proportion to the distance between the disk arrays.
Foreground Copy
Semi Sync Mode
• Updates to MV and RV are done asynchronously up to a certain
data size. When the MV update completes and data not
reflected to RV is within the predetermined data size, informs
the host of I/O completion without waiting for the RV update
and immediately reflects the update to the RV. If the data not
reflected to RV has exceeded the predetermined size, the
operation is the same as Foreground Copy (sync mode).
• This can be set only for RDR.
Background Copy -
• Updates to MV and RV are done asynchronously. After
completing the MV update, informs the host of the I/O
completion without waiting for the RV update. The RV update
is accumulated as differential information and reflected to RV
asynchronously with the MV update. The interval of copy to
RV can be set for individual disk arrays (background copy level).
3
3
3
.
.
.
6
6
6
R
R
R
V
V
V
A
A
A
c
c
c
c
c
c
e
e
e
s
s
s
s
s
s
R
R
R
e
e
e
s
s
s
t
t
t
r
r
r
i
i
i
c
c
c
t
t
t
i
i
i
o
o
o
n
n
n
S
S
S
e
e
e
t
t
t
t
t
t
i
i
i
n
n
n
g
g
g
Because RV is replicated within the disk array independently of the server, its replicated contents are
completely match with the contents of MV. When the Windows system is used, MV and RV cannot
be used at the same time within the same system, because the volume identification information used by
the Windows system to identify the volume is also the same. Data replication gives no access
restrictions for MV, allowing Read/Write (RW) at any time. For RV, set the RV access restriction in
Replicate or Restore state to Not Ready (NR) to prevent malfunctioning unless there are specific
reasons. When Read Only (RO) is set, the results vary depending on the OS and or file systems used.
So, do not set RO unless you are familiar with the OS and file system operations.