Troubleshoot file system transfers

This document describes how to troubleshoot and resolve transfer and agent issues, and where to find agent logs to help you troubleshoot issues.


The following table describes transfer error messages, and how to resolve them:

Error message Error type What the error means How to resolve the error
Modified during transfer FILE_MODIFIED_FAILURE The source file was modified during the transfer each time that Storage Transfer Service attempted to copy the source file. Prevent writes to the specified file during the next Storage Transfer Service operation.
Failed to transfer PRECONDITION_FAILURE The Cloud Storage object associated with the source file was modified each time that Storage Transfer Service attempted to upload the file. Prevent multiple transfer jobs from writing the same file to the same Cloud Storage bucket by using unique Cloud Storage object prefixes when you create transfer jobs.
Source directory not found SOURCE_DIR_NOT_FOUND Either the specified source path is incorrect, or the path is correct but not all agents have access to the path. Check the transfer job configuration and verify that:
Could not find the job's source or destination directory ROOT_DIR_NOT_FOUND Either the specified source/dest path is incorrect, or the path is correct but not all agents have access to the path. Check the transfer job configuration and verify that:
File not found FILE_NOT_FOUND_FAILURE The source file was found, but deleted before it was transferred to Cloud Storage. If the file was mistakenly deleted, restore it so that the next transfer job can upload it.
Failed to find the destination bucket BUCKET_NOT_FOUND The destination bucket doesn't exist in Cloud Storage. Verify that the destination bucket spelling is correct and that it exists.
Failed to find an internal metadata object METADATA_OBJECT_
Storage Transfer Service stores metadata in the destination bucket with the prefix storage-transfer. If the metadata files are deleted before their corresponding transfer operations complete, then this error is displayed. Avoid deleting objects with the prefix storage-transfer/ in the destination bucket until after all transfer jobs complete.
Failed due to invalid file name INVALID_FILE_NAME The path of a source file is invalid. Verify and fix the specified file path. Verify that the path uses characters that are supported by Cloud Storage.
Failed due to invalid storage class INVALID_FILE_STORAGE_CLASS The storage class for the given source does not allow reads. Find the documentation for your cloud provider to determine how to get the data into a storage class that allows copying the data out.
Failed due to invalid resumable upload session URI SESSION_URI_INVALID The resumable upload ID or session URI is expired or cancelled. The failure is being retried incorrectly. Please contact support.
Failed due to invalid file size INVALID_FILE_SIZE The file size is invalid. Verify file size is >= 0 and <= 5 TiB (max Cloud Storage object size) for transfers to Cloud Storage.
Failed due to permissions PERMISSION_FAILURE and UNAUTHENTICATED A transfer agent didn't have sufficient permissions to perform an operation. There are two possibilities for this error:
  • An agent had insufficient Google Cloud permissions.
  • An agent was unable to read a file or directory due to insufficient permissions on the source file system.

Verify the following:

Object is subject to bucket's retention policy and cannot be deleted, overwritten or archived PERMISSION_FAILURE The bucket has a retention policy in effect and the object already exists in the bucket. Storage Transfer Service cannot overwrite existing objects in the bucket. This error can be displayed if the file changed at the source, or if Storage Transfer Service attempts the upload twice due to network conditions and the first upload succeeded. Verify that the data in your Cloud Storage bucket matches your expectations. You can confirm that the size and modified time (mtime) of the source files match their Cloud Storage object counterparts by re-running the job and confirming that there are no errors.
Service lacked sufficient permissions SERVICE_PERMISSION_FAILURE Storage Transfer Service didn't have sufficient permissions to perform an operation. Storage Transfer Service uses a Google-managed service account, typically in the format of, to access resources. To determine your specific PROJECT_NUMBER, use the googleserviceaccounts.get API call. Verify that the service account has the following roles:
  • roles/storagetransfer.serviceAgent for the project.
  • roles/storage.admin for all destination buckets.
Agent unsupported AGENT_UNSUPPORTED_VERSION The agent version is no longer compatible with Storage Transfer Service. This is a temporary error, related to a bad agent update. If it occurs, do the following:
  1. Stop all of your agents.
  2. Pull the latest docker image by running: sudo docker pull
  3. Issue the Docker run command to start all of your agent containers.
If the issue persists, reach out to your support team.
Failed due to hash mismatch HASH_MISMATCH_FAILURE Each time Storage Transfer Service tried to upload this file, the uploaded bytes were corrupted. This resulted in the hash of the on-premises file not matching the hash of the resulting Cloud Storage object. This error may be caused by a number of potential issues. If you see a small percentage of hash mismatch failures (less than 1%) in a large transfer, retry the failed files. If you see a large percentage of hash mismatch failures (1% or greater), we recommend investigating potential memory, CPU, or other hardware failures on the agent machine.
Failed due to an unsupported file mode UNSUPPORTED_FILE_MODE Storage Transfer Service encountered a file with an unsupported mode, such as a device, socket, named pipe, or irregular file. Remove these special file types from the source directory.
Failed due to an error in the file system FILESYSTEM_ERROR An agent encountered a file system or operating system error when performing a file system operation such as read, seek, or stat. Read the failure description to understand which file system operation failed. Ensure the file system is accessible to the on-prem agent and responsive to basic file operations.
Failed due to an unknown error UNKNOWN_FAILURE An unexpected error occurred. Read the failure description. If the failure description does not contain sufficient information to resolve the issue, please contact support.
Failed due to an invalid specification INVALID_SPEC The agent received a corrupted internal specification. Check for data corruption on agent hosts and contact support if you cannot find any.
Failed due to an empty or invalid manifest file CONFORMANCE_FAILURE The agent cannot read or get valid CSV bytes due to invalid formatting or CSV entries. Ensure that the manifest entries are valid file paths. If the failure description does not contain sufficient information to resolve the issue, please contact support.
Falling back to resumable uploads instead of multipart uploads due to permission denied error PERMISSION_FAILURE Multipart uploads have been enabled for this transfer, but the correct permissions have not been set on the bucket. Refer to the Multipart uploads section of File system permissions for the required permissions.

Viewing agent logs

Agent logs contain information relevant to agent processes, and can help you troubleshoot agent connection problems. If your agents are listed as connected in Google Cloud console and you are experiencing transfer failures, see Viewing errors to view a sample of transfer errors. To view logs that contain a record of every file Storage Transfer Service considered during a transfer, see Viewing transfer logs.

By default, agent logs are stored in /tmp. You can change the location with the --log-dir=logs-directory command-line option.

The logs are named:



  • hostname - hostname the agent is running on.
  • username - username running the agent.
  • log-level is one of:
    • INFO - informational messages
    • ERROR - errors encountered during transfer, but that don't prevent the transfer job from continuing.
    • FATAL - errors encountered that prevent the transfer job from continuing.
  • timestamp - timestamp in YYYYMMDD-hhmmss.thread-id format.

The logs directory contains symlinks to the most recent logs for each of the priority levels:

  • agent.ERROR
  • agent.FATAL
  • agent.INFO

Slow transfer speed

If your data is taking a long time to transfer, check the following:

  1. The read throughput of your file system should be approximately 1.5 times your desired upload speed. You can use FIO to test the read throughput of your file system.

    Install fio:

     sudo apt install -y fio

    Create a new directory fiotest:

     sudo mkdir -p $TEST_DIR

    Test read throughput:

     sudo fio --directory=$TEST_DIR --direct=1
        --rw=randread --randrepeat=0 --ioengine=libaio --bs=1M --iodepth=8
        --time_based=1 --runtime=180 --name=read_test --size=1G

    After you run the commands above, Fio generates a report. The line labeled "bw" represents the total aggregate bandwidth of all threads, and it can be used as a proxy for read throughput.

  2. Use iPerf3 to check your available internet bandwidth to Storage Transfer Service.

  3. Make sure each of your transfer agents have at least 4 vCPU and 8GB of RAM.

If you've checked the conditions above and are still experiencing long transfer times, you can add additional agents to increase the number of concurrent connections to your data's file system.

For more information on how to maximize the performance of your transfer agents, see Agent best practices.

Troubleshooting agent errors

The following sections describe how to troubleshoot and resolve transfer agent errors:

Agents are not connected

If transfer agents are not displayed as connected within Google Cloud console:

  1. Verify that agents can connect to Cloud Storage APIs:

    1. Run the following command from the same machine as the transfer agent to test the agent's connection to Cloud Storage APIs:

      gsutil cp test.txt gs://my-bucket


      my-bucket with the name of your Cloud Storage bucket.

  2. If your project uses VPC Service Controls, view the agent logs for errors. If VPC Service Controls is misconfigured, the INFO agent logs will contain the following error:

    Request is prohibited by organization's policy. vpcServiceControlsUniqueIdentifier: id

    In this output:

Agents are connected but jobs fail

If agents are displayed as connected but transfer jobs fail, check the error details of the failed jobs.