Precautions For Creating A Remote Link; Functions Of Reserved Space For An Asynchronous Remote Replication Task - Huawei OceanStor V3 Series Features Manual

OceanStor V3 Series
Remote Replication Feature Guide for Block

9.6 Precautions for Creating a Remote Link

Question
What are the precautions for creating a remote link?
Answer
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9.7 Functions of Reserved Space for an Asynchronous
Remote Replication Task
Question
How do I plan reserved space for a storage pool when creating an asynchronous remote
replication task? What are the functions of reserved space?
Answer
Reserved space stores snapshots generated during asynchronous remote replication. Storage
space is reserved because:
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When configuring an asynchronous remote replication task, reserve certain space in the
storage pool of the secondary storage array to ensure that sufficient space is provided for
COW for host I/Os or data synchronization I/Os of the secondary storage array during remote
replication.
The following example shows how to plan reserved space:
The scheduled synchronization period of an asynchronous remote replication task is 1 hour,
the synchronization rate is medium (15 MB/s on average), and the host bandwidth is 5 MB/s.
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Issue 06 (2018-01-30)
If a Fibre Channel network is used, set Link Type to FC. If an IP network is used, set
Link Type to iSCSI.
If two storage systems of a remote link have different versions, initiate link creation from
the storage system of the later version. Otherwise, link creation fails.
Copy-on-write (COW) for I/Os newly written to the host during remote replication
occupies the storage pool space of the primary storage array. In addition, COW for data
synchronization I/Os of the secondary storage array occupies the storage pool space of
the secondary storage array.
If the storage pool cannot provide sufficient space, COW for host I/Os or data
synchronization I/Os of the secondary storage array fails due to insufficient space. As a
result, the remote replication session enters the split state. You are advised to reserve
30% of LUN space in an asynchronous remote replication task for copy-on-write.
Amount of data written into the host during 1 hour = 1 x 60 x 60 x 5 = 18000 MB
Time required for replicating data from the primary LUN to the secondary LUN =
18000/15 = 1200s
Amount of data written into the primary LUN when data is replicated from the primary
LUN to the secondary LUN = 1200 x 5 = 6000 MB
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