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:
  • Migrate the source server to Alibaba Cloud by generating an image in the same region, and then copy the image to the target region. For more information about how to copy an image, see Copy custom images.
  • Check whether the problem stems from the network service provider.
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.
Note The examples in this topic are for reference only.

Estimate the time required for migration

The following figure shows how to estimate the time required for migration. Where:
  • 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.
evaluate_migration_time

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:

  1. Convert units.
    • Actual data volume: 10 GB = 10 × 1024 = 10240 MB
    • Actual network speed: 10 Mbit/s = 10/8 = 1.25 MB/s
  2. Calculate the data transfer time.
    Data transfer time: 10240/1.25 = 8192 seconds = 2.27 hours
  3. Calculate the time required to create the image.
    Image creation time: 10240/30 = 341 seconds = 0.09 hours
  4. Calculate the time required for migration.
    Migration time: 2.27 + 0.09 = 2.36 hours

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.

For example:
  • 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.
Note The instance bandwidth of 1 Mbit/s displayed in the ECS console is the outbound bandwidth of the intermediate instance. The 1 Mbit/s bandwidth does not affect the actual migration speed because the inbound bandwidth of the intermediate instance is used during migration.

To test the transmission speed by using iPerf, perform the following steps:

  1. Create a pay-as-you-go ECS instance in the target Alibaba Cloud region.
  2. In the ECS instance, perform the following steps:
    1. Install iPerf.
    2. Start iPerf as a server.
    3. Add a rule to the security group of the instance to allow traffic on the ports required by iPerf.
  3. In the source server system, perform the following steps:
    1. Install iPerf.
    2. 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.

  1. Create a pay-as-you-go CentOS 7 instance in the target Alibaba Cloud region.
  2. Add an inbound rule to the security group of the ECS instance to allow traffic on the ports required by iPerf.
    This example uses the default port for iPerf, which is TCP 5001.
  3. Connect to the CentOS 7 instance.
  4. In the CentOS 7 instance, perform the following steps:
    1. Run the following command to install iPerf: 
      yum -y install iperf3
    2. Run the following command to start iPerf as a server: 
      iperf3 -s
  5. In the source server system, perform the following steps:
    1. Download and install iPerf.
    2. Run the following command to start iPerf as a client:
      Replace <Instance IP address> in the command with the public IP address of the created instance. 
      iperf3 -c <Instance IP address> -i 1 -d
  6. Wait for the iPerf test to complete and record the test results.

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.

  1. Create a pay-as-you-go Windows Server 2008 instance in the target Alibaba Cloud region.
  2. Add an inbound rule to the security group of the ECS instance to allow traffic on the ports required by iPerf.
    This example uses the default port for iPerf, which is TCP 5001.
  3. Connect to the instance.
  4. In the Windows Server 2008 instance, perform the following steps:
    1. Download and install iPerf.
    2. Open the Command Prompt.
    3. Run the cd <directory where iPerf is located> command to go to the tool directory.
    4. Run the iperf3.exe -s command to start iPerf as a server.
  5. In the source server system, perform the following steps:
    1. Download and install iPerf.
    2. Run the following command to start iPerf as a client:
      Replace <Instance IP address> in the command with the public IP address of the created instance. 
      iperf3.exe -c <Instance IP address> -i 1 -d
  6. Wait for the iPerf test to complete and record the test results.