HP StorageWorks XP24000 for FlashCopy Mirroring Software User's Guide (T5240-96001, June 2007)

Legend
1.
Write request to the
: Time flow
space from where the
data is not yet copied
S-VOL
Host
1.
Read/Write request to
the space to where the
data is not yet copied.
T-VOL
Host
S-VOL
T-VOL
3.
Write operation
Read or Write operation
3.
2.
Copy operation
(On-demand copy)
Figure 15 On-demand Copying
1. From the host
,
there is a Write request to the space in the S-VOL from which the data is not yet
copied, or there is a Read or Write request to the space in the T-VOL to which the data is
not
yet copied.
2. When a reques
t
is made to the space in the S-VOL or T-VOL from which or to which the data is
not
yet copied, Version 2 per forms on-dema nd copying before the Read or Write operation. By
on-demand
copying, the data is copied from the S-VOL to the T-VOL.
3. When on-demand c opying is completed, the Read or Write operation is performed.
Note: On-demand copying may not always be executed when there is a read request from the
host. In that case, the host will directly read the S-VOL data instead of the T-VOL data.
Warning: When the NOCOPY mode is selected, even if all the data i n the S-VOL is copied to the T-VOL
by
the on-d
emand copying process, Version 2 does not automatically withdraw the relationship. So, when
44
About
Version 2 Operations