Multipart Uploads

Multipart uploads allow you to upload large objects in parts, with better reliability and performance compared to single-request uploads.

Overview

The multipart upload process consists of three steps:

Initiate - Create a new multipart upload and receive an upload ID
Upload Parts - Upload object parts (1-10,000 parts, each 5MB-5GB)
Complete - Combine all parts into a single object

Use multipart uploads for objects larger than 100MB. Parts can be uploaded in parallel for better performance.

CreateMultipartUpload

Initiates a multipart upload and returns an upload ID.

POST /{bucket}/{key}?uploads HTTP/1.1
Host: s3.garage.example.com

Request Headers

Accepts the same metadata headers as PutObject:

Content-Type

string

MIME type for the final object

x-amz-meta-*

string

Custom metadata for the object

Cache-Control

string

Cache control directives

Checksums

x-amz-checksum-algorithm

string

Checksum algorithm to use: CRC32, CRC32C, CRC64NVME, SHA1, or SHA256

Example

AWS CLI

aws s3api create-multipart-upload --bucket my-bucket --key large-file.bin \
  --endpoint-url https://s3.garage.example.com

cURL

curl -X POST "https://s3.garage.example.com/my-bucket/large-file.bin?uploads" \
  -H "Authorization: AWS4-HMAC-SHA256 ..." \
  -H "Content-Type: application/octet-stream"

Response

<?xml version="1.0" encoding="UTF-8"?>
<InitiateMultipartUploadResult>
  <Bucket>my-bucket</Bucket>
  <Key>large-file.bin</Key>
  <UploadId>1a2b3c4d5e6f7g8h9i0j</UploadId>
</InitiateMultipartUploadResult>

UploadId

string

Hex-encoded upload identifier (use this in subsequent requests)

UploadPart

Uploads a part of the object.

PUT /{bucket}/{key}?partNumber={part-number}&uploadId={upload-id} HTTP/1.1
Host: s3.garage.example.com
Content-Length: {part-size}

Query Parameters

partNumber

integer

required

Part number (1-10,000)

uploadId

string

required

Upload ID from CreateMultipartUpload

Request Headers

Content-Length

integer

required

Size of this part in bytes (minimum 5MB except for the last part)

Content-MD5

string

Base64-encoded MD5 hash of the part data

Checksums

If a checksum algorithm was specified in CreateMultipartUpload, include the part checksum:

x-amz-checksum-crc32

string

Base64-encoded CRC32 checksum of this part

x-amz-checksum-crc32c

string

Base64-encoded CRC32C checksum of this part

x-amz-checksum-crc64nvme

string

Base64-encoded CRC64NVME checksum of this part

x-amz-checksum-sha1

string

Base64-encoded SHA1 checksum of this part

x-amz-checksum-sha256

string

Base64-encoded SHA256 checksum of this part

Example

AWS CLI

aws s3api upload-part --bucket my-bucket --key large-file.bin \
  --part-number 1 --upload-id "1a2b3c4d5e6f7g8h9i0j" \
  --body part1.bin \
  --endpoint-url https://s3.garage.example.com

cURL

curl -X PUT "https://s3.garage.example.com/my-bucket/large-file.bin?partNumber=1&uploadId=1a2b3c4d5e6f7g8h9i0j" \
  -H "Authorization: AWS4-HMAC-SHA256 ..." \
  -H "Content-Length: 10485760" \
  --data-binary @part1.bin

Response

HTTP/1.1 200 OK
ETag: "d41d8cd98f00b204e9800998ecf8427e"

Save the ETag from each UploadPart response - you’ll need them to complete the upload.

UploadPartCopy

Copies data from an existing object as a part.

PUT /{bucket}/{key}?partNumber={part-number}&uploadId={upload-id} HTTP/1.1
Host: s3.garage.example.com
x-amz-copy-source: /source-bucket/source-key

Request Headers

x-amz-copy-source

string

required

Source object path: /bucket/key

x-amz-copy-source-range

string

Byte range to copy from source: bytes=0-10485759

Example

AWS CLI

aws s3api upload-part-copy --bucket my-bucket --key large-file.bin \
  --part-number 1 --upload-id "1a2b3c4d5e6f7g8h9i0j" \
  --copy-source "/source-bucket/source-file.bin" \
  --copy-source-range "bytes=0-10485759" \
  --endpoint-url https://s3.garage.example.com

ListParts

Lists the parts that have been uploaded.

GET /{bucket}/{key}?uploadId={upload-id} HTTP/1.1
Host: s3.garage.example.com

Query Parameters

uploadId

string

required

Upload ID from CreateMultipartUpload

max-parts

integer

default:"1000"

Maximum number of parts to return (1-1000)

part-number-marker

integer

Part number to start listing from

Example

AWS CLI

aws s3api list-parts --bucket my-bucket --key large-file.bin \
  --upload-id "1a2b3c4d5e6f7g8h9i0j" \
  --endpoint-url https://s3.garage.example.com

Response

<?xml version="1.0" encoding="UTF-8"?>
<ListPartsResult>
  <Bucket>my-bucket</Bucket>
  <Key>large-file.bin</Key>
  <UploadId>1a2b3c4d5e6f7g8h9i0j</UploadId>
  <PartNumberMarker>0</PartNumberMarker>
  <NextPartNumberMarker>2</NextPartNumberMarker>
  <MaxParts>1000</MaxParts>
  <IsTruncated>false</IsTruncated>
  <Part>
    <PartNumber>1</PartNumber>
    <ETag>"d41d8cd98f00b204e9800998ecf8427e"</ETag>
    <Size>10485760</Size>
  </Part>
  <Part>
    <PartNumber>2</PartNumber>
    <ETag>"098f6bcd4621d373cade4e832627b4f6"</ETag>
    <Size>5242880</Size>
  </Part>
</ListPartsResult>

CompleteMultipartUpload

Completes the multipart upload by assembling previously uploaded parts.

POST /{bucket}/{key}?uploadId={upload-id} HTTP/1.1
Host: s3.garage.example.com
Content-Type: application/xml

Request Body

<?xml version="1.0" encoding="UTF-8"?>
<CompleteMultipartUpload>
  <Part>
    <PartNumber>1</PartNumber>
    <ETag>"d41d8cd98f00b204e9800998ecf8427e"</ETag>
  </Part>
  <Part>
    <PartNumber>2</PartNumber>
    <ETag>"098f6bcd4621d373cade4e832627b4f6"</ETag>
  </Part>
</CompleteMultipartUpload>

Part numbers must be in ascending order, but don’t need to be sequential (e.g., 1, 3, 5 is valid).

Request Headers

x-amz-checksum-crc32

string

Expected CRC32 checksum of the complete object (composite checksum)

x-amz-checksum-crc32c

string

Expected CRC32C checksum of the complete object

x-amz-checksum-sha1

string

Expected SHA1 checksum of the complete object

x-amz-checksum-sha256

string

Expected SHA256 checksum of the complete object

Example

AWS CLI

aws s3api complete-multipart-upload --bucket my-bucket --key large-file.bin \
  --upload-id "1a2b3c4d5e6f7g8h9i0j" \
  --multipart-upload "Parts=[{ETag='d41d8cd98f00b204e9800998ecf8427e',PartNumber=1},{ETag='098f6bcd4621d373cade4e832627b4f6',PartNumber=2}]" \
  --endpoint-url https://s3.garage.example.com

Response

<?xml version="1.0" encoding="UTF-8"?>
<CompleteMultipartUploadResult>
  <Location>https://my-bucket.s3.garage.example.com/large-file.bin</Location>
  <Bucket>my-bucket</Bucket>
  <Key>large-file.bin</Key>
  <ETag>&quot;abc123def456-2&quot;</ETag>
</CompleteMultipartUploadResult>

The ETag for multipart uploads has the format {md5}-{part-count}, where the MD5 is calculated from the concatenated ETags of all parts.

AbortMultipartUpload

Aborts a multipart upload and frees storage used by uploaded parts.

DELETE /{bucket}/{key}?uploadId={upload-id} HTTP/1.1
Host: s3.garage.example.com

Example

AWS CLI

aws s3api abort-multipart-upload --bucket my-bucket --key large-file.bin \
  --upload-id "1a2b3c4d5e6f7g8h9i0j" \
  --endpoint-url https://s3.garage.example.com

cURL

curl -X DELETE "https://s3.garage.example.com/my-bucket/large-file.bin?uploadId=1a2b3c4d5e6f7g8h9i0j" \
  -H "Authorization: AWS4-HMAC-SHA256 ..."

Response

HTTP/1.1 204 No Content

ListMultipartUploads

Lists in-progress multipart uploads for a bucket.

GET /{bucket}?uploads HTTP/1.1
Host: s3.garage.example.com

Query Parameters

delimiter

string

Character to group keys

encoding-type

string

Encoding for keys in response: url

key-marker

string

Key to start listing from

max-uploads

integer

default:"1000"

Maximum uploads to return (1-1000)

prefix

string

Limit to uploads for keys with this prefix

upload-id-marker

string

Upload ID to start from (for pagination)

Example

AWS CLI

aws s3api list-multipart-uploads --bucket my-bucket \
  --endpoint-url https://s3.garage.example.com

Response

<?xml version="1.0" encoding="UTF-8"?>
<ListMultipartUploadsResult>
  <Bucket>my-bucket</Bucket>
  <KeyMarker/>
  <UploadIdMarker/>
  <MaxUploads>1000</MaxUploads>
  <IsTruncated>false</IsTruncated>
  <Upload>
    <Key>large-file.bin</Key>
    <UploadId>1a2b3c4d5e6f7g8h9i0j</UploadId>
    <Initiated>2026-03-04T10:30:00.000Z</Initiated>
  </Upload>
</ListMultipartUploadsResult>

Checksum Types

When using checksums with multipart uploads, Garage supports two checksum types:

Composite Checksums

Calculated by hashing the concatenation of individual part checksums. Supported for:

CRC32
CRC32C
SHA1
SHA256

Full-Object Checksums

Calculated by combining part CRCs using CRC concatenation properties. Supported for:

CRC32
CRC32C
CRC64NVME

Specify the checksum type in the CompleteMultipartUpload request:

x-amz-checksum-type: COMPOSITE

x-amz-checksum-type: FULL_OBJECT

See AWS documentation for more details on checksum calculation.

Best Practices

Part Size

Use parts of at least 10-100 MB for optimal performance
All parts except the last must be at least 5 MB
Maximum part size is 5 GB
Maximum 10,000 parts per upload

Parallel Uploads

Upload parts in parallel to maximize throughput:

# Upload 4 parts in parallel
for i in {1..4}; do
  aws s3api upload-part \
    --bucket my-bucket \
    --key large-file.bin \
    --part-number $i \
    --upload-id "1a2b3c4d5e6f7g8h9i0j" \
    --body part${i}.bin \
    --endpoint-url https://s3.garage.example.com &
done
wait

Error Handling

Always call AbortMultipartUpload if an error occurs
Use ListParts to verify uploaded parts before completing
Set up lifecycle rules to automatically abort incomplete uploads after a timeout

Checksums

Use checksums for data integrity verification
Choose CRC variants for better performance
Use SHA variants when cryptographic strength is needed

Complete Example

Here’s a complete workflow using the AWS CLI:

# 1. Initiate upload
UPLOAD_ID=$(aws s3api create-multipart-upload \
  --bucket my-bucket \
  --key large-file.bin \
  --endpoint-url https://s3.garage.example.com \
  --output text --query 'UploadId')

# 2. Upload parts (example: 2 parts)
ETAG1=$(aws s3api upload-part \
  --bucket my-bucket \
  --key large-file.bin \
  --part-number 1 \
  --upload-id "$UPLOAD_ID" \
  --body part1.bin \
  --endpoint-url https://s3.garage.example.com \
  --output text --query 'ETag')

ETAG2=$(aws s3api upload-part \
  --bucket my-bucket \
  --key large-file.bin \
  --part-number 2 \
  --upload-id "$UPLOAD_ID" \
  --body part2.bin \
  --endpoint-url https://s3.garage.example.com \
  --output text --query 'ETag')

# 3. Complete the upload
aws s3api complete-multipart-upload \
  --bucket my-bucket \
  --key large-file.bin \
  --upload-id "$UPLOAD_ID" \
  --multipart-upload "Parts=[{ETag=$ETAG1,PartNumber=1},{ETag=$ETAG2,PartNumber=2}]" \
  --endpoint-url https://s3.garage.example.com

Documentation Index

​Overview

​CreateMultipartUpload

​Request Headers

​Checksums

​Example

​Response

​UploadPart

​Query Parameters

​Request Headers

​Checksums

​Example

​Response

​UploadPartCopy

​Request Headers

​Example

​ListParts

​Query Parameters

​Example

​Response

​CompleteMultipartUpload

​Request Body

​Request Headers

​Example

​Response

​AbortMultipartUpload

​Example

​Response

​ListMultipartUploads

​Query Parameters

​Example

​Response

​Checksum Types

​Composite Checksums

​Full-Object Checksums

​Best Practices

​Complete Example

​See Also

Overview

CreateMultipartUpload

Request Headers

Checksums

Example

Response

UploadPart

Query Parameters

Request Headers

Checksums

Example

Response

UploadPartCopy

Request Headers

Example

ListParts

Query Parameters

Example

Response

CompleteMultipartUpload

Request Body

Request Headers

Example

Response

AbortMultipartUpload

Example

Response

ListMultipartUploads

Query Parameters

Example

Response

Checksum Types

Composite Checksums

Full-Object Checksums

Best Practices

Complete Example

See Also