S3cmd uploads an object in multiparts by default. The unit of each part is MB, and each part ranges from 5 MB to 5120 MB. The default part size is 15 MB. The size of each part can be set using either of the following methods:
If an object is larger than the configured part size, S3cmd uploads it in multiparts in multiple threads. If any part fails to be uploaded, S3cmd retries uploading only the failed part and other parts will not be affected.
Users can also disable multipart upload using the --disable-multipart parameter. For details, see section Uploading an Object.