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

About ShadowImage™ for IBM
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z/OS
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Operations 2-19
Hitachi ShadowImage™ for IBM
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z/OS
®
User’s Guide
Note: Make sure that the Swap&Freeze option remains in effect until the pair
status becomes duplex after the quick restore operation.
Figure 2-9 shows the state of the T-VOL after the quick restore operation with
or without the Swap&Freeze option.
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Figure 2-9 Quick Restore Operation With or Without Swap&Freeze
Option
The Quick Restore pairresync operation on a pair which status is split
exchanges the data in the S-VOL and the T-VOL of the pair. If you use
Swap&Freeze option when performing the Quick Restore pairresync operation,
the update copy operation will not take place after the Quick Restore
pairresync operation is complete. Therefore, the data of the S-VOL and the
T-VOL is kept exchanged. If you do not use Swap&Freeze option when
performing the Quick Restore pairresync operation, the update copy operation
will take place after the Quick Restore pairresync operation is complete, and
the data in the S-VOL overwrites the T-VOL.
Host I/O Performance Option
The Host I/O Performance option is used to improve host I/O responses over
SIz copying processing time. When the Host I/O Performance option is in
effect, the storage system suppresses execution of SIz copying processing,
and consequently host I/O responses improve.
Note:
When SIz copying processing is suppressed by the Host I/O
Performance option, the time taken for copying increases. Also, if
ShadowImage pairs exist, host I/O responses might not be improved. In this
case, set the Host I/O Performance option for ShadowImage as well.
Copy Threshold Option
If the load of USP V storage system increases, host server I/O performance
(response) may be degraded. If ShadowImage for z/OS performs copy
operations when the load of the storage system is heavy, it is more likely that
host server I/O performance (response) may be degraded. The Copy
Threshold option temporarily stops SIz copy operations when the load of the
storage system is heavy. If you set this option in effect, you can minimize the
degradation of host I/O performance by temporarily stopping SIz copy
operations when the load of the storage system is heavy.