HP XP7 Storage - Manual (Page 22)

Figure 16 Preserve Mirror Compatible FlashCopy function
The two methods to establish a Compatible FlashCopy relationship using the Preserve Mirror
Compatible FlashCopy function are:
•
REQUIRED: Perform the copying operation only when the Compatible FlashCopy relationship
can be established using the Preserve Mirror Compatible FlashCopy function. When the
relationship cannot be established, the command is rejected.
•
PREFERRED: Perform the copying operation using the Compatible FlashCopy-to-PPRC primary
volume function even if the Compatible FlashCopy relationship cannot be established using
the Preserve Mirror Compatible FlashCopy function. In this case, the Cnt Ac-S Z pair status
becomes Pending.
When you use the Preserve Mirror Compatible FlashCopy function, note the following:
•
Cnt Ac-S Z is required.
•
Only Cnt Ac-S Z synchronous pairs can be used.
•
The two Cnt Ac-S Z pairs must be in Duplex status. If they are not in Duplex, the operation
differs depending on the specified option (PRESMIRREQ or PRESMIRRPREF).
•
It is recommended that you set the missing interrupt handler (MIH) timer to 45 seconds when
working with Cnt Ac-S Z synchronous pairs.
•
If you create Cnt Ac-S Z pairs or resynchronize suspended pairs when Compatible FlashCopy
relationships exist, Compatible FlashCopy prepares as many copies as the number of
relationships. The larger the number of relationships per volume, the longer it takes for Cnt
Ac-S Z pairs to become Duplex. Even with lower load, it takes approximately 1.5 times as
much time as when the Cnt Ac-S Z pairs are not used with FlashCopy.
When using the Preserve Mirror FlashCopy function, it is recommended that the maximum
number of relationships (or data sets) per volume should be 2000 or less. If that is not possible,
you should create and operate one relationship for each volume. This causes non-data-set
parts to be copied as well, but the status of the Cnt Ac-S Z pairs will change to Duplex in a
shorter time.
Caution:
•
When you establish Compatible FlashCopy relationships with Preserve Mirror Compatible
FlashCopy function in COPY mode, a relationship is established in both the MCU and the
RCU, but the progress of the copy operations for the relationship in the MCU and the
relationship in the RCU are not synchronized. If you issue Withdraw during the copy operation,
both of the Compatible FlashCopy relationships are suspended. Therefore, the consistency of
the data between P-VOL and S-VOL is not ensured even though the Cnt Ac-S Z pair is in Duplex
status. This status is confirmed by the PPRC CQUERY command to a Cnt Ac-S Z volume or the
Cnt Ac-S Z Pair Operation window of Remote Web Console. To release this status, delete the
Cnt Ac-S Z pair.
•
If the relationship in the local site cannot be established, the relationship in the remote site
could be established, depending on the type of error. Even if you try again to create a
Compatible FlashCopy relationship using the Preserve Mirror Compatible FlashCopy function,
22 About Compatible FlashCopy