Before you start to migrate your servers, you must evaluate your services, the time required for migration, and related costs to develop an appropriate migration plan. This topic describes the major factors that you need to evaluate.

Operating systems

  • Kernel version: CentOS 5 or later, Red Hat 5 or later, Ubuntu 10 or later, or Windows Server 2003 or later. If your kernel version is earlier than the preceding versions listed, you must upgrade your kernel to a supported version.
  • Virtualized driver: The KVM virtio driver must be installed.
  • Required services and software: For Linux systems, rsync is required and curl is recommended. For Windows systems, the Volume Shadow Copy Service (VSS) must be operating properly.
  • Grand Unified Bootloader (GRUB): For operating systems with earlier kernel versions such as CentOS 5, Red Hat 5, and Debian 7, GRUB must be upgraded to V1.99 or later.
  • Disk size: The system disk must be 40 GiB to 500 GiB in size, and the data disks must be 20 GiB to 32,768 GiB in size.

Application services

  • Service suspension: If you are running large service applications such as Oracle, SQL Server, MongoDB, MySQL, and Docker databases, we recommend that you suspend them before starting the migration. If such service applications cannot be suspended, we recommend that you exclude the corresponding data directories from the migration, and then wait until the server migration is complete to synchronize the databases.
  • Large data volume: If there is a large number of data files, we recommend that you migrate only the server application environment. You can then evaluate whether to migrate the files through a leased line or Data Transport for faster transfer speeds.
  • Software licensing: You must evaluate whether licensed software in the source system will require a new license after migration.
  • Network configuration: The public IP address changes after migration. You must evaluate whether this will affect the original services.

Network mode

You need to evaluate the network transfer mode required for the server system to be migrated.

The server migration process includes three phases:
  1. Pre-migration resource preparation
  2. Data transfer
  3. Post-migration configuration
By default, the Internet is used in phases 1, 2, and 3. Therefore, the server to be migrated must have access to the following Alibaba Cloud service endpoints and ports:
  • Phases 1 and 3:
    • ECS: https://ecs.aliyuncs.com:443. For more information about endpoints, see Request structure.
    • VPC: https://vpc.aliyuncs.com:443.
    • STS: https://sts.aliyuncs.com:443.
  • Phase 2: transfer of data through the public IP address and ports 8080 and 8703 of the temporary intermediate instance
Additionally, the Alibaba Cloud migration service supports the following transfer modes for specific network environments:
  • Default transfer over the Internet: By default, the Internet is used in Phases 1, 2, and 3.
  • Manual transfer over VPCs: The Internet is used in Phases 1 and 3 and VPCs are used in Phase 2.

    Manual transfer over VPCs applies to the server systems that can access the specified VPC but cannot access the preceding Alibaba Cloud service endpoints. In this case, you must prepare an additional server system of the same type that can access the preceding Alibaba Cloud service endpoints to facilitate the migration. For more information, see VPC-based migration.

  • Automatic transfer over VPCs: The Internet is used in Phases 1 and 3 and VPCs are used in Phase 2.

    Automatic transfer over VPCs applies to the server systems that can access the preceding Alibaba Cloud service endpoints and the specified VPC. This mode also applies to the server systems whose data is transferred over VPCs in Phase 2. Automatic transfer over VPCs requires simpler operations as compared with manual transfer over VPCs. For more information, see VPC-based migration.

Quantity of servers to migrate

If you need to migrate multiple servers at a time, take note of the following points:
  1. Before migration:
    • Contact your local network operator to confirm the traffic limits, or set the upper limit of the transmission bandwidth by using Server Migration Center (SMC).
    • Submit a ticket to request an increase of your Alibaba Cloud quotas on images and pay-as-you-go resources such as vCPUs.
  2. During migration:
    • Check whether the server systems support automated batch O&M to distribute and run the Cloud Migration tool on multiple servers.
    • Evaluate whether you need to collect statistics on and analyze the batch migration progress logs.
  3. After migration:
    • Evaluate how to configure the migrated server systems in batches.
    • Evaluate how to validate the configurations of migrated server systems.

Migration period

The migration period is proportional to the number of servers that you migrate and the actual data volume. We recommend that you estimate the migration period by conducting tests in advance.

The migration period is composed of the time required for three phases: before migration, during migration, and after migration. You can calculate the time required for each phase as follows:
  • Time required before migration
    • Time required before migration = Time taken to prepare for the migration
    • The amount of time taken to prepare for the migration varies based on the actual conditions.
  • Time required during migration
    • Time required during migration = Data transfer time + Image production time (optional)
    • Data transfer time = Actual data volume/Actual network speed
    • Image production time = Actual data volume/Snapshot service speed
    Note By default, the Cloud Migration tool enables compression during data transfer. This results in a transfer rate increase by 30% to 40%. The image production time depends on the speed of the snapshot service of Alibaba Cloud, which can be from 10 MB/s to 30 MB/s.
  • Time required after migration
    • Time required after migration = Incremental system synchronization time after migration (optional) + System configuration validation time
    • Incremental system synchronization time = Actual incremental data volume/Actual network speed
    • The system configuration validation time varies based on the actual conditions.
Note By default, the migration service generates a full image. If you want to minimize the migration period, you can also migrate data directly to the destination instance. For more support, contact the migration service technical support personnel of Alibaba Cloud.

Migration costs

The Cloud Migration tool is provided free of charge. However, you will be charged for resources used during migration. During the migration, an ECS instance with the default name INSTANCE_FOR_GOTOALIYUN is created automatically under your Alibaba Cloud account to act as an intermediate instance. This intermediate instance is a pay-as-you-go instance. Ensure that you have enough account balance in your linked bank card.

Note After the migration is complete, all resources on the intermediate instance, including the cloud disks, are automatically released. If the migration fails, the intermediate instance will be retained in your ECS console for your next migration attempt. If you do not want to continue with the migration, we recommend that you manually release the intermediate instance to avoid incurring unnecessary fees.