Basic behavior – HP StorageWorks XP Remote Web Console Software User Manual
Page 83
Note that the 3DC cascading configuration of XP Continuous Access Journal and XP Continuous
Access Synchronous is not available in the system that consists of multiple primary and secondary
storage systems.
The response time for host I/Os will roughly be the sum of the response time for XP Continuous
Access Synchronous operation and the creation time of journal data in an intermediate site.
The utilization rate of the primary site in the 3DC cascading configuration will be greater than a
configuration consisting of only a data volume that is being replicated with XP Continuous Access
Synchronous.
Basic Behavior
This section explains the basic behavior of a 3DC cascading configuration under the following
conditions:
•
The status of the XP Continuous Access Synchronous pair is PAIR. The status of the XP Continuous
Access Journal pair is also PAIR.
•
A host in the primary site issues an I/O request to the XP Continuous Access Synchronous
P-VOL.
As illustrated in
, if a host in the primary site issues an I/O request, the following
operations are completed:
•
Data will be stored in the XP Continuous Access Synchronous P-VOL.
•
Data will also be stored in the XP Continuous Access Synchronous S-VOL (that is, the XP
Continuous Access Journal primary data volume).
◦
After that, the fact that data has been stored will be reported to the primary site.
◦
The fact that I/O has been finished will be reported to the host.
•
Data in the XP Continuous Access Journal primary data volume (that is, the XP Continuous
Access Synchronous S-VOL) will be stored as journal data in the master journal volume in the
intermediate site.
Sequence numbers, which indicate the order that data will be written, will be added to the
journal data.
•
Journal data in the master journal volume in the intermediate site will be transferred,
independently from and asynchronously with the behavior mentioned above, to the restore
journal volume in the secondary site.
•
Next, the journal data in the restore journal volume will be restored to the XP Continuous
Access Journal secondary data volume in the secondary site.
Journal data will be restored in the order of the sequence numbers that are added to the
journal data. These sequence numbers ensure that updates to XP Continuous Access Journal
secondary data volumes at the secondary site will be made in the same order that updates to
the XP Continuous Access Synchronous P-VOL in the primary site are made.
As explained above, when the host in the primary site issues an I/O request to the XP Continuous
Access Synchronous P-VOL, the data will be restored asynchronously to the XP Continuous Access
Journal secondary data volume in the secondary site at a remote location.
Interoperability with Other Products and Functions
83