HP StorageWorks XP Remote Web Console Software - Manual (Page 95)

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Specifying COPY mode or NOCOPY mode
Before starting the copy operation, FlashCopy Mirror Version 2 allows you to select the mode to run the
copy operation between COPY mode and NOCOPY mode. When you do not select the mode, FlashCopy
Mirror Version 2 automatically selects COPY mode.
When you select COPY mode, FlashCopy Mirror Version 2 copies all the data in the S-VOL to the T-VOL.
This process is called “background copying”. FlashCopy Mirror Version 2 automatically withdraw the pair
when the background copying is complete. Note that when you select NOCOPY mode, FlashCopy Mirror
Version 2 omits the background copying process.
If there is a request for write operation to the space in the S-VOL from where the data is not yet copied or
a request for read/write operation to the space in the T-VOL to where the data is not yet copied, FlashCopy
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 43 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.