Multipart upload

R2 supports S3 API’s Multipart Upload ↗ with some limitations.

Limitations

Object part sizes must be at least 5MiB but no larger than 5GiB. All parts except the last one must be the same size. The last part has no minimum size, but must be the same or smaller than the other parts.

The maximum number of parts is 10,000.

Most S3 clients conform to these expectations.

Lifecycles

The default object lifecycle policy for multipart uploads is that incompleted uploads will be automatically aborted 7 days. This can be changed by configuring a custom lifecycle policy.

ETags

The ETags for objects uploaded via multipart are different than those uploaded with PutObject.

For uploads created after June 21, 2023, R2’s multipart ETags now mimic the behavior of S3. The ETag of each individual part is the MD5 hash of the contents of the part. The ETag of the completed multipart object is the hash of the MD5 sums of each of the constituent parts concatenated together followed by a hyphen and the number of parts uploaded.

For example, consider a multipart upload with two parts. If they have the ETags bce6bf66aeb76c7040fdd5f4eccb78e6 and 8165449fc15bbf43d3b674595cbcc406 respectively, the ETag of the completed multipart upload will be f77dc0eecdebcd774a2a22cb393ad2ff-2.

Note that the binary MD5 sums themselves are concatenated and then summed, not the hexadecimal representation. For example, in order to validate the above example on the command line, you would need do the following:

echo -n $(echo -n bce6bf66aeb76c7040fdd5f4eccb78e6 | xxd -r -p -)\
$(echo -n 8165449fc15bbf43d3b674595cbcc406 | xxd -r -p -) | md5sum