NOTE
The DCL is stored on all the disks in the disk domain and four-disk RAID 1 is used for data protection
while storage system logs are stored on coffer disks.
When synchronization is started (synchronization is manually started or automatically triggered when
the system reaches the synchronization period), snapshots of the primary and secondary LUNs are
generated and activated. Snapshot functions are as follows:
l
Primary LUN snapshot
Ensures that data read from the primary LUN during data synchronization is always consistent and
allows for simultaneous implementation of data synchronization and data write to the primary
LUN.
l
Secondary LUN snapshot
Stores backup data for the data on the secondary LUN before synchronization so that data on the
secondary LUN is still usable even if a failure occurs during synchronization.
The snapshot function is used only during data synchronization. After data synchronization is complete,
the snapshot function stops to reduce system overhead and improve performance.
1.
The host sends a write I/O request to the RM, and the RM directly writes data to the
primary cache.
2.
The primary cache returns the write I/O result to the RM, and the RM further returns the
result to the host.
3.
After data in the primary cache is written to the LUN, the RM records data differences
between the primary LUN and the secondary LUN in the DCL.
4.
When a replication period starts, the snapshots of the primary and secondary LUNs are
activated.
5.
Data is replicated from the primary cache and LUN to the secondary cache.
Asynchronous remote replication employs multi-time-point caching technology to
replicate data from cache to the DR site. The working principle is as follows:
a.
When a replication period starts, new time segments (T2 and P2) are respectively
generated in the caches of primary and secondary LUNs.
b.
New data from the host is written to time segment T2 in the cache of the primary
LUN.
c.
The primary LUN returns a message indicating that the write I/O operation is
complete.
d.
Data in time segment T1 is replicated to time segment P2.
e.
Data in the caches of the primary and secondary LUNs is written to LUNs.
6.
The RM deletes differences recorded in the DCL after replicating data.
7.
After the remote replication, the snapshot for the primary and secondary LUNs is
stopped.
1.3.3 Service Switchover
When a disaster occurs at the primary site of a remote replication session, the secondary site
can quickly take over primary site services to ensure business continuity.
The remote replication feature not only implements remote data backup but also recovers
services as soon as possible in the case of a disaster to keep service continuity. The following
two indicators need to be considered before a service switchover:
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RPO
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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