HP XP P9500 Storage - Manual (Page 142)

The host issues an update to the Cnt Ac-S primary volume (P-VOL), which is copied synchronously
to the S-VOL. The Cnt Ac-J system copies the synchronous S-VOL data to the Cnt Ac-J remote site.
Data in the Cnt Ac-J S-VOL is an asynchronous copy of the Cnt Ac-S P-VOL. Depending on RPO
and bandwidth, Cnt Ac-J S-VOL data can be very close to P-VOL data. As always with Cnt Ac-J,
data consistency is ensured.
Figure 21 3-data-center cascade configuration
Failure recovery occurs as follows:
•
If a failure occurs at the Cnt Ac-S P-VOL, business continues because data in the Cnt Ac-J
S-VOL is restored to the production system via the intermediate volume, if needed. Update
sequence integrity is ensured.
•
If a failure occurs at both Cnt Ac-S P-VOL and S-VOL, an implemented disaster recovery plan
would re-direct host activities to the Cnt Ac-J S-VOL.
See “Recovery for 3 Cnt Ac-J/Cnt Ac-S DC cascade configuration ” (page 97) for recovery
information and procedures.
Prerequisite information for 3DC cascade
•
P9500 must be installed at the local, Cnt Ac-S intermediate, and Cnt Ac-J remote sites.
•
RAID Manager is recommended at all sites.
•
Remote Web Console is required at all sites.
Host application ◦
◦ Cnt Ac-S
◦ Cnt Ac-S primary volume (P-VOL), the primary production volume
◦ Cnt Ac-S fence level must be Data .
•
The intermediate site requires the following:
Cnt Ac-S ◦
◦ Cnt Ac-J
◦
Cnt Ac-S S-VOL = Cnt Ac-J P-VOL
◦ Cnt Ac-J master journal volume
•
The remote site requires the following:
Cnt Ac-J ◦
◦ Cnt Ac-J S-VOL
◦ Cnt Ac-J remote journal volume
•
Differential data is used to re-synchronize a suspended Cnt Ac-S or Cnt Ac-J pair.
•
When the Cnt Ac-S pair is recovered, the Cnt Ac-J pair in PAIR or COPY status is automatically
split by the system.
142 Configurations with Continuous Access Synchronous