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Figure 2-51:
Synchronous replication performed by Storage Replica 
Note In Figure 2-51, T indicates data flushed to the volume at the source site, and T1 indicates 
data flushed to the volume at the remote site. In all cases, logs always write through. 
Asynchronous replication 
In contrast to synchronous replication, asynchronous replication means that when the application 
writes data, that data replicates to the remote site without immediate acknowledgment guarantees 
(see Figure 2-52). This mode facilitates faster response time to the application as well as a DR solution 
that works geographically. With its higher-than-zero Recovery Point Objective (RPO), asynchronous 
replication is less suitable for HA solutions such as failover clusters because they are designed for 
continuous operation with redundancy and no loss of data. 
Figure 2-52: 
Asynchronous replication performed by Storage Replica 

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CHAPTER 2 | Software-defined datacenter 
As Figure 2-52 illustrates, when the application writes data (1), the replication engine captures and 
logs the write (2) and immediately acknowledges to the application (3). The captured data then 
replicates to the remote location (4). The remote node processes the copy of the data, writes log data 
(5), and lazily acknowledges back to the source copy (6). Because replication performance is no longer 
in the application I/O path, the remote site’s responsiveness and distance are less important factors. 
There is risk of data loss if the source data is lost while the destination copy of the data is still in buffer 
without leaving the source. 
Implementation-specific details 
Storage Replica utilizes SMB 3.0 as a reliable, high-speed data transport for replication. This grants all 
the advantages of SMB 3.0, such as multichannel, RDMA, encryption, signing, and Kerberos-based 
security. Storage Replica does not require any changes to Active Directory Domain Services (AD DS) or 
any domain administrative permissions. The following table summarizes the implementation-specific 
details of Storage Replica: