The migration period is divided into three parts: pre-migration, migration, and post-migration. The migration period is proportional to the number of servers to be migrated and the actual data volume. We recommend that you estimate the migration time by conducting tests in advance. This topic describes how to estimate the time required for migration and how to test the transmission speed.
Background information
During an SMC-based migration, the system first creates an intermediate instance under your account. Then, the system transfers data from the source server to the intermediate instance and creates an Alibaba Cloud ECS image of the intermediate instance. Therefore, the migration time is equal to the sum of the data transfer time and the image creation time. For more information, see Estimate the time required for migration.
During the migration process, the speed of transmission from the source server to the intermediate instance is the primary factor that determines the migration time. For more information about how to test the transmission speed, see Test the transmission speed.
In some cases, the data transmission speed is lower than the actual measured one. The following table lists the possible causes and solutions.
Possible cause | Solution |
---|---|
The source server and the intermediate instance are in different regions or countries. Network transmission across regions and countries is sometimes slower than that in the same region. |
Check whether the network for the source server is the same as that for the intermediate
instance in the target Alibaba Cloud region. If the problem is caused by cross-region
transmission, you can perform the following operations:
|
The source server has performance bottlenecks. For example, limited CPU, memory, and disk performance results in poor SMC transmission efficiency. | Improve the performance of the source server. For example, you can improve the CPU, memory, and disk performance. |
By default, the SMC client uses the single-threaded data transfer model, which may have bottlenecks in some network environments. | Enable multi-threaded transfer acceleration to maximize bandwidth utilization. For more information, see Enable multi-threaded transfer acceleration. |
Estimate the time required for migration
- The speed for creating a snapshot is about 30 MB/s.
- For more information about how to test the network speed, see Test the transmission speed.

If you have a server with an actual disk usage of 10 GB and an outbound bandwidth of 10 Mbit/s, you can use the following method to estimate the migration time:
Test the transmission speed
The speed of transmission from the source server to the intermediate instance is determined by the outbound bandwidth of the source server and the inbound bandwidth of the intermediate instance. By default, the inbound bandwidth of the intermediate instance is 200 Mbit/s. You can submit a ticket to increase the bandwidth.
- If the outbound bandwidth of the source server is 100 Mbit/s and the inbound bandwidth of the intermediate instance is 200 Mbit/s, the actual transmission speed is limited by the source server, and does not exceed 100 Mbit/s.
- If the outbound bandwidth of the source server is 300 Mbit/s and the inbound bandwidth of the intermediate instance is 200 Mbit/s, the actual transmission speed is limited by the intermediate instance, and does not exceed 200 Mbit/s.
To test the transmission speed by using iPerf, perform the following steps:
- Create a pay-as-you-go ECS instance in the target Alibaba Cloud region.
- In the ECS instance, perform the following steps:
- Install iPerf.
- Start iPerf as a server.
- Add a rule to the security group of the instance to allow traffic on the ports required by iPerf.
- In the source server system, perform the following steps:
- Install iPerf.
- Start iPerf as a client. Set the IP address of the destination server to the public IP address of the pay-as-you-go instance created in step 1.
Example of performing a transmission speed test on a Linux instance
The following example uses a CentOS 7 instance. The operations may vary with the version of your operating system.
Example of performing a transmission speed test on a Windows instance
The following example uses a Windows Server 2008 instance. The operations may vary with the version of your operating system.