HP XP P9500 Storage - Manual (Page 9)

the old data is copied from the S-VOL to the T-VOL first, and then the read/write operation is
performed. This process is called on-demand copying. The following figure shows the process of
on-demand copying.
Figure 3 On-demand copying
1. From the host, there is a write request to an S-VOL from where the data has not been copied,
or there is a Read or Write request to the space in the T-VOL to where the data has not been
copied.
2. When an operation as described is made to the space in the S-VOL or T-VOL where the data
has not been copied, Compatible FlashCopy 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.
On-demand copy may not always be executed when there is a read request from the host. In that
case, the host directly reads the S-VOL data instead of the T-VOL data.
WARNING! 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, Compatible FlashCopy SE does not automatically
withdraw the relationship. Therefore, when you selected NOCOPY mode, you must withdraw the
pair by using the FCWITHDR command. If you select the NOCOPY2COPY mode for the relationship
made by NOCOPY mode, the background copying process is performed. When all the data are
copied, the relationship is released automatically.
Copy modes 9