HP StorageWorks XP Remote Web Console Software - Manual (Page 54)

2-32 Chapter 3 Preparing for Universal Replicator z/OS Operations
Hitachi Universal Replicator for IBM /OS User’s Guide
In Figure 2-8, because a failure occurs in the primary site A, Business
Continuity Manager is used to change the former TCz Synchronous secondary
site to the primary site B. If you perform delta resync operation in this
situation, the URz pair for delta resync operation in Figure 2-7 will be
synchronized and usable.
When you perform delta resync operation, first the journal data in the primary
site B are copied to the URz secondary site by journal copy. In this journal
copy, only the journal data which is not yet restored to the secondary data
volume in the URz secondary site are copied in chronological order. When the
journal copy completes, journal restore takes place in the URz secondary site.
In delta resync operation, the status of the URz pair will not change to Pending
Duplex but Duplex. This is because delta resync operation copies only the
really necessary data by journal copying. Compared to the usual way which
copies the whole data in the primary data volume, delta resync operation
requires shorter time for the recovery of the URz pair after a failure occurs.
Note: When the total capacity of stored journal data exceeds 80% of the
journal volume of TCz Synchronous secondary site, old journal data will be
deleted automatically. Therefore, if the total capacity of the journal data which
is not restored to the URz secondary data volume exceeds 80% of the journal
volume, the secondary data volume will not be able to be restored completely
by copying the journal data to the restore journal volume in the URz
secondary site. In that case, according to the setting of the journal group
option, whole data in the primary data volume will be copied to the secondary
data volume, or delta resync operation finishes without any processing.
Usually, if the pair between TCz Synchronous primary site and secondary site
is synchronized periodically, the total capacity of the journal data which is not
restored to the URz secondary site will not exceed 80% of the journal volume.
Though, for example if the URz pair is suspended and the pair has not been
resynchronized for a long time, journal data of more than 80% of the journal
volume capacity may be stored before they are restored to URz secondary
data volume. In such case, note that you may not perform delta resync
operation properly.
Warning: Even if the capacity of the journal data does not exceed 80% of the
journal volume, note that journal data will or may be destroyed in the
following cases.
• When you restore the TCz Synchronous pair, then updated the M-VOL
• When you restore the URz pair between the primary site and the URz
secondary site, then updated the M-VOL
• When the retry processing occurs because of a delay of the M-VOL update
• When the update of the TCz Synchronous R-VOL is delayed