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After an asynchronous remote replication task is created, initial synchronization is
performed to copy full data from the primary LUN to the secondary LUN. After the
initial synchronization is complete, if the remote replication pair is normal, incremental
data of the primary LUN will be synchronized to the secondary LUN based on the
specified synchronization mode (manual or automatic). If the remote replication is
interrupted due to a fault, incremental data will be synchronized from the primary to the
secondary LUN based on the specified recovery policy (manual or automatic) after the
fault is rectified.
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After a synchronous remote replication task is created, initial synchronization is
performed to copy full data from the primary LUN to the secondary LUN. After the
initial synchronization is complete, if the remote replication pair is normal, host I/Os will
be written into both the primary and secondary LUNs, not requiring data
synchronization. If the remote replication is interrupted due to a fault, incremental data
will be synchronized from the primary to the secondary LUN based on the specified
recovery policy (manual or automatic) after the fault is rectified.
Synchronization can be classified into the following three scenarios based on the types of
primary and secondary LUNs:
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The primary LUN is a thin LUN not configured with SmartDedupe&SmartCompression
and the secondary LUN is a thin LUN with no space allocated. During the initial
synchronization, data for which space is not allocated on the primary LUN will not be
synchronized to the secondary LUN.
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The primary LUN is a thick LUN or a thin LUN configured with
SmartDedupe&SmartCompression and the secondary LUN is a thin LUN with no space
allocated. During the initial synchronization, data in the primary LUN is read in
sequence and the consecutive 64 KB all zero data will not be synchronized to the
secondary LUN.
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In other scenarios except the previous two, during the initial synchronization, the system
reads data in the primary LUN in sequence. The 64 KB all zero data is compressed to 4
KB (16:1), synchronized to the secondary LUN, decompressed to 64 KB, and then
written to the secondary LUN. Other data is written to the secondary LUN in sequence.
Splitting
Splitting is a process of stopping replicating data from the primary to the secondary LUN.
This operation can be performed only by the administrator. Splitting can be performed for a
single remote replication session or multiple remote replication sessions in a consistency
group at one time. After the splitting, the pair relationship between the primary LUN and the
secondary LUN still exists and the access permission of hosts for the primary and secondary
LUNs remains unchanged.
At some time, for example when the bandwidth is not enough to support critical services, you
probably do not want to copy data from the primary LUN to the secondary LUN. In such
cases, you can split the secondary LUN from the primary LUN to suspend data
synchronization.
Users can effectively control a remote replication process by performing synchronization and
splitting.
Primary/Secondary Switchover
A primary/secondary switchover is a process of exchanging the roles of the primary and
secondary LUNs in a pair relationship. You can perform a primary/secondary switchover for a
OceanStor V3 Series
Remote Replication Feature Guide for Block
1 Feature Description
Issue 06 (2018-01-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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