HP XP P9500 Storage - Manual (Page 130)

B Continuous Access Journal configurations with Continuous
Access Synchronous
Continuous Access Journal and Continuous Access Synchronous can share the same data volumes.
Using Continuous Access Journal and Continuous Access Synchronous can extend disaster recovery
options to a third data center.
This chapter provides planning formation for sharing Continuous Access Journal volumes with
Continuous Access Synchronous. It describes four Continuous Access Journal/Continuous Access
Synchronous configurations.
In this appendix, P-VOL indicates the primary volume, and S-VOL indicates the secondary volume.
These terms are used for both Continuous Access Journal and Continuous Access Synchronous.
Sharing volumes with Continuous Access Synchronous
Like Continuous Access Journal, a Continuous Access Synchronous pair maintains a copy of the
production volume in a second location. However, unlike Continuous Access Journal, the Continuous
Access Synchronous secondary volume (S-VOL) is synchronous, and the remote system is located
within the same general region as the local site.
Creating a Continuous Access Journal backup and a Continuous Access Synchronous backup
insures that a copy in a third location is available in the event that the primary site, and possibly
one of the secondary sites, fail.
Continuous Access Journal and Continuous Access Synchronous can be used and configured in a
variety of ways. The following describes four principle configurations. These are covered in detail
in this appendix.
•
In a 3 Data Center Cascade configuration (3DC Cascade), three data centers are used —
the Continuous Access Synchronous production site, the Continuous Access
Synchronous/Continuous Access Journal intermediate site, and the distant Continuous Access
Journal remote site. The figure in the
“3DC cascade configuration ” (page 131) provides an
illustration. With this configuration, you can locate the Continuous Access Synchronous
synchronous site near the local site to lower I/O response time, while the Continuous Access
Journal backup provides a disaster recovery solution at a remote site.
•
In a 3 Data Center multitarget configuration (3DC multitarget), the production volume is shared
by the Continuous Access Synchronous and Continuous Access Journal. This volume is the
primary volume (P-VOL) for both at the local site. The targets of each system are located at
different remote sites. They provide the Continuous Access Synchronous solution and the
Continuous Access Journal asynchronous disaster recovery solution. The Continuous Access
Synchronous secondary site is at an intermediate location, the Continuous Access Journal
secondary site is at a distant location. This is illustrated in
“3DC multitarget configuration ”
(page 132) .
•
Another use of the 3DC multitarget is the Continuous Access Journal Delta Resync pair, which
provides a quick way to regain a long distance copy after disaster in the event that the
Continuous Access Synchronous/Continuous Access Journal P-VOL becomes unusable. In this
case, the host continues I/O operations at the intermediate Continuous Access Synchronous
S-VOL site. With a second Continuous Access Journal pair previously set up between the
Continuous Access Synchronous S-VOL and the Continuous Access Journal S-VOL, only
differential data needs to be copied to the Continuous Access Journal S-VOL. Delta resync is
illustrated in
“3DC multitarget configuration ” (page 132) .
•
In a 2 Data Center configuration (2DC), data is copied from the Continuous Access Synchronous
P-VOL to an intermediate site, though not to the Continuous Access Synchronous S-VOL. Instead,
the data is copied to the Continuous Access Journal master journal volume. This results in an
asynchronous copy that side-steps the Continuous Access Synchronous S-VOL, and thus
enhances overall transfer speed to the Continuous Access Journal S-VOL. This is illustrated in
“2 data center configuration ” (page 140) .
130 Continuous Access Journal configurations with Continuous Access Synchronous