HP XP Continuous Access Software - Manual (Page 20)

View Advanced Edition Software or XP Remote Web Console software products do not provide
host failover functions.
When using XP Continuous Access Journal as a data migration tool, host failover is recommended
but not required. When using XP Continuous Access Journal as a disaster recover tool, host failover
is required to ensure effective disaster recovery operations. When an XP Continuous Access Journal
pair is suspended due to an error condition, the primary array generates sense information that
should be transferred to the remote site using the host failover software for effective disaster detection
and recovery.
Remote copy operations
Figure 5 (page 20) illustrates the types of XP Continuous Access Journal remote copy operations:
initial copy and update copy.
Figure 5 Remote copy operations
Initial copy operations
Initial copy operations synchronize data in the primary data volume with data in the secondary
data volume and are performed independently from host I/Os. Initial copy operations are performed
when creating a data volume pair or when resynchronizing a suspended pair. The initial copy
operation copies base-journal data obtained from the primary data volume at the primary array
to the secondary array, and then restores the base-journal to the secondary data volume.
The journal-obtain operation uses all of the primary data volume's data as base-journal data, in
sequence. The base-journal contains a replica of the entire data volume and a replica of data
volume updates. The base-journal is copied from the primary array to the secondary array after
the secondary array issues a read-journal command. After the base-journal is copied to the
secondary array, the base-journal is stored in a restore journal volume in a restore journal group
to which the secondary data volume belongs. After that, data in the restore journal volume is
restored (destaged) to the secondary data volume, so data in the secondary data volume is
representative of data in the primary data volume.
Base-journal data reflects the entire data volume plus updates. The difference area within the
base-journal is used during differential resynchronization operations. Journal data for the entire
data volume is created when the data volume pair is created. Difference journal data is used when
the data volume's pair status changes from Suspended to Pairresync. Merging difference bitmaps
recorded in regards to the primary and secondary data volumes allows you to obtain out-of-order
data for only what changed while the pair was suspended. When a data volume pair is suspended,
20 Overview of XP Continuous Access Journal