Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access XP P9000 for Linux B.12.00.00

mode, noting changed tracks in a bitmap for future resynchronization. Recovery typically involves
a destructive process such as rewriting all the changed tracks, with possible loss of data consistency
for ordered writes.
In contrast, Continuous Access Journal logs every change to the journal disk at the primary site,
including the metadata required to apply the changes consistently. If the replication link between
sites fail, Continuous Access Journal keeps logging changes in the local journal so that they can
be transmitted later, without interruption to the protection process or the application. The journal
data is simply transferred after the network link failure or bandwidth limitation is corrected, with
no loss of consistency. The recovery time might be extended a bit during temporary link failures
or congestion, but the asynchronous replication process does not fail, and the catch-up process is
simple and automatic. Data consistency is preserved.
With Continuous Access Journal, the remote storage system pulls data from the primary journal
volumes over the data replication network as fast as the bandwidth allows while adjusting to
available network conditions. If the available bandwidth does not support optimal replication, such
as during peak-load spikes in transaction volume, the primary journal volumes buffer the data on
disk until more bandwidth becomes available.
Journal group
The journal group is a component of the Continuous Access Journal operations that consists of two
or more data and journal volumes. The data update sequence from the host is managed per the
journal group. This ensures the data update sequence consistency between the paired journal
groups is maintained.
Journal groups are managed according to the journal group number. The paired journal numbers
of journal groups can be different. One journal group can have more than one data volume and
journal volume.
NOTE: Metrocluster with Continuous Access XP P9000 for Linux supports only one journal group
pair per package. Thus, in a Metrocluster, the number of packages that can be configured to use
journal group is limited by the maximum number of journal groups that are supported by the XP
or P9000 in the configuration, or by the maximum number of packages in the cluster, whichever
is smaller.
Continuous Access journal pair state
If the amount of data in the journal cache, in the secondary subsystem, reaches the specified journal
cache capacity, the secondary subsystem stores the received journal data into the restore journal
volume, and then issues the next read-journal command to the primary subsystem. This suppresses
the increase in the cache usage rate.
The Continuous Access Journal retains the PAIR state when the Continuous Access links fail as
long as the journal volumes have enough space while the Continuous Access Asynchronous switches
to PSUE state.
In addition, this allows host write-data to be kept continuously as journal data in the journal volumes
while the updated data is not being replicated to the remote array. Once the links are recovered,
the data replication of the primary and secondary arrays is resumed automatically. The journal
data accumulated in the primary journal volumes is replicated automatically to the secondary site
.
NOTE: If the journal volumes reach full capacity, the pair state is switched to PFUS and the data
written to the data volume is tracked in bitmap.
RAID Manager Instance
HP Storage XP or P9000 RAID Manager (XP or P9000 RAID Manager) is a software that enables
you to configure and control data replication and data protection on XP or P9000 disk arrays.
10 Introduction