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OceanStor 18500, 18800, and 18800F Storage System V100R001C30 Remote Replication Feature Guide 09

This document describes the remote replication feature, in terms of the implementation principle, application scenario, configuration process, and reference information.
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Restrictions

Restrictions

This section describes the impact of the remote replication feature on system performance, interaction between the remote replication feature and other features, and restrictions on the remote replication feature.

Impact on Host Performance

  • Synchronous remote replication: The secondary site synchronizes data with the primary site in real time. In this case, host performance is affected by the comparatively long data transmission latency. Specifically, the primary site can return a response indicating that the I/O processing is completed to the host only after the secondary site completes the I/O processing.
  • Asynchronous remote replication: The secondary site synchronizes data with the primary site periodically. In this case, host performance is not affected. However, in the event of a disaster, the amount of lost data is mainly subject to the synchronization period. (A longer synchronization period leads to more lost data. A shorter synchronization period leads to less lost data.) I/O requests delivered by a host are processed only at the primary site. When the user-defined synchronization period reaches, a data synchronization is automatically initiated between the primary site and the secondary site. Therefore, after completing the I/O processing, the primary site immediately returns a response indicating that the I/O processing is completed to the host.

Impact on Other Features

The remote replication feature is a LUN-based data protection feature. Before using this feature and another feature at the same time, you should consider whether the features can share LUNs. For example, in one storage system, if LUN01 has been used as the secondary LUN of a clone pair, LUN01 cannot be used as the primary LUN of a remote replication session at the same time. Table 1-5 lists the relationship between value-added features in terms of the LUN use, helping you plan the use of LUNs in a scenario where multiple features are enabled simultaneously.
Table 1-5  Relationship between value-added features in terms of the LUN use
LUN Used by Other Feature

Primary LUN of a Remote Replication Session

Secondary LUN of a Remote Replication Session

Snapshot source LUN

a

Snapshot LUN

×b

×

Primary LUN of a clone pair

Secondary LUN of a clone pair

×

×

Source LUN of a LUN copy

Target LUN of a LUN copy

×

×

Source LUN of a SmartMigration

×

×

Target LUN of a SmartMigration

×

×

Mirror LUN of HyperMirror

Mirror Copies of HyperMirror

×

×

eDevLUNs that are hosted using SmartVirtualiztaion

a: indicates that the two LUNs are not mutually exclusive.

b: × indicates that the two LUNs are mutually exclusive.

If you select an existing LUN to be the secondary LUN or target LUN of a value-added feature, data on the existing LUN may be overwritten. Therefore, perform this operation with caution.

Application Restriction

  • The remote replication feature is not available if network address translation (NAT) devices exist on the local area network (LAN) where the storage system resides.
  • The remote replication feature of this series does not support direct data replication with a storage device from another vendor.
  • If you want to apply the remote replication feature to a LUN, you need to reserve some capacity in the storage pool where the LUN resides:
    • Reserve 0.5% of the LUN capacity when applying the synchronous remote replication to save metadata.
    • Reserve 30.5% of the LUN capacity when applying the asynchronous remote replication. The reserved capacity consists of two parts. One part accounts for about 0.5% and is used to save metadata. The other part is used for copy-on-write and you are advised to reserve 30%. For details about capacity planning, see Functions of Reserved Space for an Asynchronous Remote Replication Task.
  • If you want to apply multiple features such as remote replication, HyperClone, SmartMigration, HyperMirror, HyperSnap, and HyperMetro to a LUN, you need to reserve some capacity in the storage pool where the LUN resides:
    • Reserve 1% of the LUN capacity when applying the synchronous remote replication to save metadata.
    • Reserve 31% of the LUN capacity when applying the asynchronous remote replication. The reserved capacity consists of two parts. One part accounts for about 1% and is used to save metadata. The other part is used for copy-on-write and you are advised to reserve 30%. For details about capacity planning, see Functions of Reserved Space for an Asynchronous Remote Replication Task.
  • Table 1-6 lists the maximum distance between the primary site and secondary site supported by the remote replication feature.
Table 1-6  Maximum distance supported by the remote replication feature

Networking Mode

Synchronous remote replication

Asynchronous Remote Replication

Direct connection using iSCSI host ports

100 m to 150 m

100 m to 150 m

Direct connection using Fiber Channel host ports (multi-mode optical fibers)

500 m

500 m

Connection through remote transfer devices (switches or routers)

200 km

No restriction

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Updated: 2019-01-28

Document ID: EDOC1000077758

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