Switching Over Owning Controllers of LUNs
OceanStor storage systems support switchover of owning controllers on local LUNs. The
switchover on the primary storage switches over owning controllers of primary LUNs. The
switchover on the secondary storage switches over owning controllers of secondary LUNs. In
parallel networking, it is recommended to set the same owning controller for primary and
secondary LUNs of a remote replication pair. For example, if primary LUNs belong to
controller A, secondary LUNs also belong to controller A. If primary and secondary LUNs
have different owning controllers, I/O forwarding is required, affecting performance.
1.3.2 Data Replication
Data replication is a process of writing service data generated by hosts to the secondary LUN
in the secondary storage system for backup and disaster recovery. The writing process varies
depending on the remote replication mode. This section describes data replication performed
using synchronous and asynchronous remote replication sessions.
Writing Process in Synchronous Remote Replication
A synchronous remote replication session replicates data in real time from the primary storage
system to the secondary storage system. The characteristics of synchronous remote replication
are as follows:
l
After receiving a write I/O request from a host, the primary storage system sends the
request to the primary and secondary LUNs.
l
The data write result is returned to the host only after the data is written to both primary
and secondary LUNs. The data write result is determined by whether the data is
successfully written to the primary LUN and is irrelevant to the secondary LUN. If data
fails to be written to the primary LUN or secondary LUN, the primary LUN or secondary
LUN returns a write I/O failure to the remote replication management module. Then, the
remote replication management module changes the mode from dual-write to single-
write, and the remote replication is interrupted.
After a synchronous remote replication pair is created with the primary LUN and the
secondary LUN, you need to manually perform synchronization so that the two LUNs are
consistent. Every time a host writes data to the storage system after synchronization, the data
is copied from the primary LUN to the secondary LUN in real time.
shows how a
synchronous replication processes a write (N: Data block being written).
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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