HP StorageWorks XP Remote Web Console Software - Manual (Page 38)

Storing Journal at the Secondary Storage System
A secondary storage system receives the journal data that is transferred from a primary storage system
according to the read journal command. The journal data will be stored into the cache at first, and
then into the journal volume.
The primary storage system does not remove the target journal data from its master journal volume until it
receives the sequence numbers of restored journal which is give to the read journal command from the
secondary storage system. This is true even if the primary storage system and secondary storage system
are connected via a channel extender product.
Selecting and Restoring Journal at the Secondary Subsystem
The secondary subsystem selects journal data to be promoted to formal data (or " restored") as follows:
1. The secondary subsystem gives the number as the management information to distinguish the
journal data arrival to the sequence number that is assigned to the journal data from the primary
subsystem. If the number is 1, the journal data arrived at the secondary subsystem. If the number
is 0, the journal data has not arrived yet. The secondary subsystem determines whether the
journal data should be settled or not according to this number. If the journal data has not
arrived yet, the secondary subsystem waits for the journal data.
2. When the top of queue in the journal group indicates the journal data arrival, the secondary
subsystem selects the journal data which has the lowest sequence number, and then settles
this journal data.
3. The secondary subsystem repeats steps (1) and (2) to select and settle the journal data.
This diagram shows that journal data S1 arrives at the secondary subsystem because the management
information indicates 1. The secondary subsystem selects journal data S1 to be settled, because S1 is the
lowest sequence number. When S1 is removed from the queue of sequence numbers, journal data S2
becomes the top entry, but it has not arrived yet. The management information of journal data S2 is 0.
The secondary subsystem waits journal data S2. When journal data S2 arrives, the secondary subsystem
selects S2 as the next journal data to be settled. The journal data selected by the secondary subsystem is
marked as “host-dirty” and treated as formal data.
38 Overview of Universal Replicator Operations