HP XP7 Storage - Manual (Page 134)

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When the delta resync P-VOL is updated, and then the journal volume at the Cnt Ac-S remote
site exceeds 70%.
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When the delta resync pair is created and no volumes (including volumes after failover or
failback) in the local site are updated.
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When the status of the Cnt Ac-J pair for delta resync operation becomes HLDE, the journal
data necessary for the delta resync operation might be discarded. In this case, all data in the
delta resync P-VOL would be copied to the delta resync S-VOL.
2 data center configuration
In a 2DC configuration, update data is transferred from the Continuous Access Synchronous P-VOL
to the Continuous Access Journal master journal volume, and then to the Cnt Ac-J S-VOL.
Though there are three sites, data is not copied to the Cnt Ac-S S-VOL in the intermediate site, only
the journal volume. Thus it is called, “2 data center”, or 2DC.
Figure 19 2 data center (2DC)
The Cnt Ac-J S-VOL contains the same data as the Cnt Ac-S P-VOL. If failure occurs, business tasks
are taken over using the Cnt Ac-J S-VOL.
The master journal in the intermediate site is registered with the 2DC Cascade setting enabled.
This setting prevents host data from being written to the Cnt Ac-J P-VOL/Cnt Ac-S S-VOL. Data in
the master journal receives Cnt Ac-J sequence numbering for write order and is pulled by the Cnt
Ac-J remote site to the S-VOL.
Drive capacity can be minimized using the virtual volume of Thin Provisioning (THP V-VOL) as the
data volume in the intermediate site. The THP V-VOL is associated with the pool volume, which
has a smaller capacity and thus lowers drive capacity. For information on THP V-VOLs, see HP
XP7 Provisioning for Open Systems User Guide.
Prerequisite information for 2DC configuration
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XP7 must be installed at the local, Cnt Ac-S intermediate, and Cnt Ac-J remote sites.
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RAID Manager is recommended at all sites. If the intermediate site is not connected to a host,
a remote command device is required. See HP XP7 RAID Manager User Guide for more
information.
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Remote Web Console is required at all sites.
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The local site requires the following:
Host application ◦
◦ Cnt Ac-S
◦ Cnt Ac-S P-VOL, the primary production volume.
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The intermediate site requires the following:
Cnt Ac-S
◦
◦ Cnt Ac-J
◦ Cnt Ac-S S-VOL = Cnt Ac-J P-VOL
134 Configurations with Continuous Access Synchronous