HP XP Business Copy Software - Manual (Page 32)

operation is performed without the Swap&Freeze option, the P-VOL and S-VOL are resynchronized
when update copy operations are performed for pairs in PAIR status.
The following figure shows the state of the S-VOL after the quick restore operation with or without the
Swap&Freeze option.
Figure 11 Quick Restore operation with or without Swap&Freeze option
.
The Quick Restore pairresync operation on a pair with status of PSUS exchanges data in the pair's
P-VOL and S-VOL. If you use the 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, data on the P-VOL and S-VOL is kept exchanged. If you do not use the
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 data on the
P-VOL overwrites data on the S-VOL.
Host I/O Performance option
This option prioritizes host I/O responses over BC copy processing time. When you use the Host I/O
Performance option, the disk array suppresses execution of BC copy processing, and consequently
host I/O responses improve.
When BC copy processing is suppressed, the time taken for copying increases. Also, if ShadowImage
for z/OS pairs exist, host I/O responses might not be faster. In this case, set the Host I/O Performance
option for ShadowImage for z/OS as well.
Cascade function
This function creates a second layer of volume pairs underneath the first layer of BC pairs. Pairs
created in the first and second layer are called cascaded pairs.
Figure 12 illustrates cascaded BC
volume pairs. The first cascade layer (L1) is the original BC pair, consisting of one P-VOL (root volume)
and up to three S-VOLs (node volumes). In the second cascade layer (L2), the S-VOLs of the original
BC pair function as the P-VOLs of the L2 pairs, and each L2 P-VOL can have up to two S-VOLs (leaf
volumes). This layering scheme can create up to nine copies of one BC primary volume (P-VOL).
Business Copy XP (BC) for the Array 32