3DC cascade configuration
As illustrated below, the Continuous Access Synchronous P-VOL is the primary production volume
in a 3DC cascade configuration. The Continuous Access Synchronous S-VOL is located at an
intermediate site that is near the primary site.
The host issues an update to the Continuous Access Synchronous primary volume (P-VOL), which
is copied synchronously to the S-VOL. The Continuous Access Journal system copies the synchronous
S-VOL data to the Continuous Access Journal remote site.
Data in the Continuous Access Journal S-VOL is an asynchronous copy of the Continuous Access
Synchronous P-VOL. Depending on RPO and bandwidth, Continuous Access Journal S-VOL data
can be very close to P-VOL data. As always with Continuous Access Journal, data consistency is
insured.
Figure 19 3DC cascade (3DC cascade)
Failure recovery occurs as follows:
• If a failure occurs at the Continuous Access Synchronous P-VOL, business continues because
data in the Continuous Access Journal S-VOL is restored to the production system via the
intermediate volume, if needed. Update sequence integrity is insured.
• If a failure occurs at both Continuous Access Synchronous P-VOL and S-VOL, an implemented
disaster recovery plan would redirect host activities to the Continuous Access Journal S-VOL.
See “Recovery in a 3DC cascade configuration ” (page 97) for recovery information and
procedures.
Prerequisite information for 3DC cascade
• P9500 must be installed at the local, Continuous Access Synchronous intermediate, and
Continuous Access Journal remote sites.
• RAID Manager is recommended at all sites.
• Remote Web Console is required at all sites.
Host application◦
◦ Continuous Access Synchronous
◦ Continuous Access Synchronous primary volume (P-VOL), the primary production volume
◦ Continuous Access Synchronous fence level must be Data.
• The intermediate site requires the following:
Continuous Access Synchronous◦
◦ Continuous Access Journal
◦ Continuous Access Synchronous S-VOL = Continuous Access Journal P-VOL
◦ Continuous Access Journal master journal volume
3DC cascade configuration 135
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