Hitachi ShadowImage for IBM z/OS User"s Guide (T5213-96002, June 2007)

2-12 About ShadowImage™ for IBM
®
z/OS
®
Operations
Hitachi ShadowImage™ for IBM
®
z/OS
®
User’s Guide
Caution: Even if the copy operation is completed without any host I/O, the
data in the S-VOL and the data in the T-VOL may not be the same. Whether
the S-VOL and the T-VOL have the same data depends on the condition of the
storage system. To make the S-VOL data and the T-VOL data equal, split the
pair and make the pair status split.
• Reverse Copy (backward pairresync in normal speed)
The reverse copy operation (see Figure 2-7) synchronizes the S-VOL with
the T-VOL. The copy direction for a reverse copy operation is T-VOL to
S-VOL. The pair status during a reverse copy operation is resync-r, and the
S-VOL and T-VOL become inaccessible to all hosts for write operations
during a reverse copy operation. As soon as the reverse copy operation is
complete, the S-VOL becomes accessible.
• Quick Restore (backward pairresync in fast speed)
The quick restore operation (see Figure 2-7) speeds up the reverse copy
operation by changing the volume map in the USP V storage system to
swap the contents of the S-VOL and T-VOL without copying the T-VOL data
to the S-VOL. The S-VOL and T-VOL are resynchronized when update copy
operations are performed for pairs in the duplex status.
The pair status during a quick restore operation is resync-r until the
volume map change is complete. The S-VOL and T-VOL become
inaccessible to all hosts for write operations during a quick restore
operation.
Notes:
– After quick restore operation is executed, the Storage Navigator window
may display old configuration information on components such as
logical volumes (LDEVs); the window may display configurations before
the quick restore operation is performed. To refresh configuration
information on the Storage Navigator window, wait until the quick
restore operation completes, click File, and then Refresh on the menu
bar of the window.
– If the differential data between S-VOL and T-VOL is small, the reverse
copy operation may be completed faster than the quick restore
operation.
Figure 2-7 illustrates the example of how the data changes during the
backward pairresync operations.