HP XP Business Copy Software - Manual (Page 104)

104 ShadowImage for the XP1024/XP128/XP12000/XP10000/SVS 200
Mirror Version 2 first copies the old data in the S-VOL to the T-VOL. This process is called “on-demand
copying”. The figure below illustrates the process of the on-demand copying.
Figure 49 On-demand Copying
1. From the host, there is a write request to the space in the S-VOL from where the data is not yet copied,
or there is a Read or Write request to the space in the T-VOL to where the data is not yet copied.
2. When there is a request shown above is made to the space in the S-VOL or T-VOL from or to where the
data is not yet copied, FlashCopy Mirror Version 2 performs on-demand 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 copying is completed, the Read or Write operation is performed.
NOTE: On-demand copy might not always be executed when there is a request from the host. In that
case, the host directly reads the S-VOL data instead of the T-VOL data.
CAUTION: When the NOCOPY mode is selected, even if all the data in the S-VOL is copied to the T-VOL
by the on-demand copying process, the FlashCopy Mirror Version 2 does not automatically withdraw the
pair. So, when you selected NOCOPY mode, you must withdraw the pair by using FCWITHDR command.
For details about FCWITHDR command, see ” Withdrawing FlashCopy Mirror Version 2 Pairs: FCWITHDR ”
on page 137.
Volume Copying and Dataset Copying
FlashCopy Mirror Version 2 allows you to select the two types of copying. One type is the volume copying,
which copies the whole volume. Another type is the dataset copying, which copies only the specified copy
range (extent). While the volume copying establishes the relationship with the entire volume, the dataset
copying establishes the relationship only to the specified extent or extents. You can specify the multiple
extents.