3. The RM concurrently writes the write I/O request to both the primary cache and
secondary cache.
4. The primary cache and secondary cache return the write I/O result to the RM.
5. After receiving the response from the primary cache and secondary cache, a storage
array returns the write I/O result to the host. If data fails to be written to the primary
cache or secondary cache, the primary cache or secondary cache returns a write I/O
failure to the RM. The RM then changes the mode from dual-write to single-write and
the remote replication is interrupted.
6. The storage array determines whether dual-write succeeds.
– If data has been successfully written to both the primary cache and secondary
cache, the LOG is deleted.
– If data fails to be written to the primary cache or secondary cache, the LOG is
stored in the DCL.
Writing Process in Asynchronous Remote Replication
Asynchronous remote replication sessions periodically replicate data from the primary to
secondary storage systems. The principles of asynchronous remote replication are as follows:
l Asynchronous remote replication relies on the snapshot technology. A snapshot is a
point-in-time copy of source data.
l When a host successfully writes data to a primary LUN, the primary storage system
returns a response to the host declaring the successful write.
l Data synchronization is triggered manually or automatically at configured intervals.
When an asynchronous remote replication relationship is configured between primary and
secondary LUNs, an initial synchronization begins. The initial synchronization copies all data
from the primary to the secondary LUN to ensure data consistency.
When a host is writing to the primary storage system, the primary storage system sends the
data to the primary LUN. If the write is successful, a response message will be sent from the
primary LUN to the primary storage system and then to the host. At configured
synchronization times, new data is copied from the primary to the secondary LUN. Figure
1-3 shows the writing process in asynchronous remote replication mode (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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