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COS Migration

Last updated: 2022-06-28 15:45:00


    COS Migration is an all-in-one tool that integrates the COS data migration feature. You can use it to migrate local data to COS through simple configurations and steps. It has the following features:

    • Checkpoint restart: Restarting uploads from checkpoints is supported. For large files, if the upload exits halfway or service failure occurs, you can run the tool again to restart the upload.
    • Multipart upload: An object can be uploaded to COS by parts.
    • Parallel upload: Multiple objects can be uploaded at the same time.
    • Migration verification: Migrated objects can be verified.

    • COS Migration only supports UTF-8 encoding.
    • If you use this tool to upload a file that already has the same name, the existing file will be overwritten. You need to configure the tool to skip files with the same name.
    • Use the migration service platform preferably for scenarios other than local data migration.

    Operating Environment

    Operating system

    Windows, Linux, and macOS.

    Software dependency

    • JDK 1.8 x64 or later. For more information, see Java.
    • IFUNC needs to be supported on Linux and the binutils version should be later than 2.20.

    How to Use

    1. Get the tool

    Download COS Migration here.

    2. Decompress the package


    Decompress the package and save it to a directory, for example:



    Decompress the package and save it to a directory, for example:

    unzip cos_migrate_tool_v5-master.zip && cd cos_migrate_tool_v5-master

    Migration tool structure

    The structure of the properly decompressed COS Migration tool is as follows:

    |——conf  #Directory of the configuration file
    |   |——config.ini  #Migration configuration file
    |——db    #Store the record of successful migrations
    |——dep   #JAR package generated by compilation of the main logic of the program
    |——log   #Log generated during tool execution
    |——opbin #Script for compilation
    |——src   #Source code of the tool
    |——tmp   #Temporary file storage directory
    |——pom.xml #Project configuration file
    |——README  #Readme document
    |——start_migrate.sh  #Migration start script for Linux
    |——start_migrate.bat #Migration start script for Windows

    • The db directory mainly records the IDs of files successfully migrated by the tool. Each migration job will first compare the records in the db directory. If the ID of the current file has already been recorded, the current file will be skipped; otherwise, it will be migrated.
    • The log directory keeps all the logs generated during tool migration. If an error occurs during migration, check error.log in this directory first.

    3. Modify the config.ini file

    Before running the migration start script, modify the config.ini file (path: ./conf/config.ini) first. This file contains the following parts:

    3.1 Configure the migration type

    type indicates the migration type, which you need to enter based on your migration needs. For example, to migrate local data to COS, configure type=migrateLocal for [migrateType].


    Currently, the following migration types are supported:

    Migration Type Description
    migrateLocal Migration from local system to COS.

    3.2 Configure the migration job

    You can configure a migration job based on your actual needs, including its destination COS bucket information.

    # The common configuration section of the migration tool includes account information to be migrated to the destination COS bucket.
    Name Description Default Value
    secretId SecretId of your key. Replace the value of COS_SECRETID with your key information, which can be obtained on the API key management page in the CAM console. -
    secretKey SecretKey of your key. Replace the value of COS_SECRETKEY with your key information, which can be obtained on the API key management page in the CAM console. -
    bucketName Name of the destination bucket in the format of <bucketname-appid>. The bucket name must contain the APPID, such as examplebucket-1250000000. -
    region Region information of the destination bucket. For the abbreviations for COS regions, see Regions and Access Endpoints. -
    storageClass Storage class for the migrated data. Valid values: Standard, Standard_IA, Archive. For more information, see Storage Class Overview. Standard
    cosPath COS path to migrate to. / indicates to migrate to the root path of the bucket, and /folder/doc/ indicates to migrate to /folder/doc/ in the bucket. If /folder/doc/ does not exist, a path will be created automatically. /
    https Whether to transfer over HTTPS. Valid values: on: Yes; off: No. It takes time to enable transfer over HTTPS, which is suitable for scenarios that demand high security. off
    tmpFolder The directory used to store temporary files when data is migrated from another cloud storage service to COS, which will be deleted after the migration is completed. The format must be an absolute path:
    Linux uses a slash (/) as the delimiter, for example, /a/b/c.
    Windows uses two backlashes (\) as the delimiter, for example, E:\\a\\b\\c.
    The default value is the tmp directory in the path of the tool.
    smallFileThreshold Number of bytes as the threshold for small files. If the size is greater than or equal to this threshold, multipart upload will be used; otherwise, simple upload will be used. Default value: 5 MB 5242880
    smallFileExecutorNum Concurrency for uploading small files (smaller than smallFileThreshold) via simple upload. Decrease the concurrency if files are uploaded to COS over the public network with a low bandwidth. 64
    bigFileExecutorNum Concurrency for uploading large files (greater than or equal to smallFileThreshold) via multipart upload. Decrease the concurrency if files are uploaded to COS over the public network with a low bandwidth. 8
    entireFileMd5Attached The migration tool calculates the MD5 of the entire file and stores it in the x-cos-meta-md5 custom header of the file for subsequent verification, because the ETag of a large file uploaded to COS via multipart upload is not the MD5 of the entire file. on
    daemonMode Whether to enable daemon mode. Valid values: on: Yes; off: No. In daemon mode, the program will keep performing synchronization. The synchronization interval is configured by the daemonModeInterVal parameter. off
    daemonModeInterVal Time interval in seconds between two rounds of synchronization. 60
    executeTimeWindow Execution time window with a granularity in minute, which defines the time period when the migration tool runs jobs. For example:
    03:30,21:00 means that jobs will be executed between 03:30 and 21:00, and the tool will be in sleep mode at other times, when the migration will be paused and the progress will be retained until the next time window when the migration will resume automatically.
    outputFinishedFileFolder This directory stores the results of successful migration jobs, and the result files are named by date, for example, ./result/2021-05-27.out, where ./result is the created directory. Each line in the result files is in the format of "Absolute path"\t"File size"\t"Last modified time". If outputFinishedFileFolder is left empty, no results will be output. ./result
    resume Whether to continue with the result of the last run and traverse through the list of files from the source. The tool starts from scratch by default. false
    skipSamePath Whether to skip the existing file if a file with the same name already exists in COS. By default, the tool does not skip the existing file; that is, it overwrites the existing file. false

    3.3 Configure the data source

    Configure each section according to the migration type described in [migrateType]. For example, if [migrateType] is configured as type=migrateLocal, you will only need to configure the [migrateLocal] section.

    3.3.1 Configure a local data source migrateLocal

    To migrate from a local system to COS, configure this section. The specific configuration items and descriptions are as follows:

    # Configuration for migration from a local system to COS
    Configuration Item Description
    localPath Absolute path of the local directory
    • Linux uses a slash (/) as the delimiter, for example, /a/b/c.
    • Windows uses two backlashes (\) as the delimiter, for example, E:\\a\\b\\c.
    excludes Absolute path of the directory or file to be excluded, indicating some directories or files under localPath are not to be migrated. Multiple absolute paths need to be separated by semicolons. If this is left blank, all files under localPath will be migrated.
    ignoreModifiedTimeLessThanSeconds Exclude files that have an update time less than a certain period of time from the current time (in seconds). This item is left blank by default, indicating files are not to be filtered by the time specified by lastmodified. It is suitable for scenarios where you run the migration tool while updating files and don't want files being updated to be migrated to COS. For example, if it is configured as 300, only files updated at least 5 minutes ago will be uploaded.

    4. Run the migration tool


    Double-click start_migrate.bat to run the tool.


    1. Run the following command to read the configuration from the config.ini file:

      sh start_migrate.sh
    2. Run the following command to read the configuration from command lines for some parameters:

      sh start_migrate.sh -Dcommon.cosPath=/savepoint0403_10/

    • The tool supports reading configuration items in two ways: command line or configuration file.
    • The command line takes priority over the configuration file, i.e., for the same configuration item, parameters in command lines take priority.
    • Reading configuration items from command lines allows you to run different migration jobs at the same time, provided that key configuration items (such as bucket name, COS path, and source path to be migrated) in the two jobs are not exactly the same. Concurrent migration can be achieved because different migration jobs are written into different db directories. Refer to db information in the tool structure above.
    • Configuration items are in the format of -D{sectionName}.{sectionKey}={sectionValue}. sectionName is the section name of the configuration file. sectionKey is the name of the configuration item in the section. sectionValue is the value of the configuration item in the section. The COS path to which data is to be migrated should be in the format of -Dcommon.cosPath=/bbb/ddd.

    Migration Mechanism and Process

    Migration mechanism

    COS Migration has a status. Successful migrations will be recorded in the format of KV in the leveldb file under the db directory. Before each migration, check whether the path to which data is migrated has been recorded in the db directory. If yes, and its attribute is the same as that in db, the migration will be skipped; otherwise, the migration will be executed. The attribute varies by migration type. For local migration, mtime determines whether to migrate. For migration from other cloud storage services and bucket replication, the etag and length of the source file determine whether to migrate. Therefore, we search for records of successful migrations in the db directory rather than in COS. If a file is deleted or modified via COSCMD or the console rather than the migration tool, the migration tool cannot detect this change, and the file will not be re-migrated.

    Migration process

    1. The configuration file is read, the configuration section is read according to the migration type, and parameters are checked.
    2. The IDs of the files to be migrated are scanned and compared in the db directory according to the specified migration type to determine whether upload is allowed.
    3. The execution results are printed out during migration, where inprogress indicates migration is in progress, skip indicates skipped, fail indicates failed, ok indicates succeeded, and condition_not_match indicates file fails to meet migration conditions (such as lastmodified and excludes) and is skipped. Details about the failure can be viewed in the error log. The execution process is as shown below:
    4. Statistics are printed out after the migration is completed, which include the total number of migrated, failed, and skipped files as well as the amount of time consumed. In case of failures, check the error log or rerun the migration job as the migration tool will skip successfully migrated files and retry migrating failed ones. The execution result of a migration job is as shown below:


    If an exception such as migration failure or execution error occurs when you use the COS Migration, troubleshoot as instructed in COS Migration.

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