Troubleshooting the S3 multipart part too small alert

The S3 multipart part too small alert is triggered if an S3 client attempts to complete a multipart upload with parts that do not meet Amazon S3 size limits.

Before you begin

About this task

StorageGRID enforces Amazon S3 size limits for multipart parts. S3 clients must follow these guidelines:

If the S3 multipart part too small alert is triggered, you must inform S3 client users to modify their request settings. To give clients time to adjust their multipart upload settings, you can run a script to temporarily disable the enforcement of minimum part size.


  1. Use the tenant ID shown in the alert details to identify the tenant account.
  2. Use the client IP address shown in the alert details to identify the specific S3 client.
  3. Inform all client users that each part in a multipart upload must be between 5 MiB and 5 GiB. Only the last part can be smaller than 5 MiB (5,242,880 bytes).
  4. Optionally, temporarily disable the minimum size restriction for StorageGRID:
    1. Log in to the primary Admin Node: ssh admin@grid_node_IP
    2. Enter the password from Passwords.txt.
    3. Switch to root: su-
    4. Run this script:'/usr/local/mgmt-api/app/scripts/s3-multipart-part-size-enforcement.rb --disable'
      (Use --enable to undo this change.)
      Note: This script will be removed in StorageGRID 11.5. After you upgrade to StorageGRID 11.5, all S3 clients must use part sizes between 5 MiB and 5 GiB.
  5. To determine if an S3 client has successfully updated their multipart upload requests.
    1. Ask the client to upload a test object.
    2. Go to ILM > Object Metadata Lookup, and look up the object.
    3. Confirm that the size of each part (segment) is greater than 5 MiB (5,242,880 bytes).
  6. If you disabled the size restriction, look for S3 multipart upload requests in which the parts are too small (requests that previously would have failed):
    1. Access the /var/local/log/bycast-err.log file.
    2. Grep the log file.
      • Grep for the tenant ID to find errors related to a specific S3 tenant account.
      • Grep for EntityTooSmall to find requests that would have failed if minimum size checking were enabled.