ECS 3.6.2 Data Access Guide

Overwriting part of an object

You can use ECS extensions to the S3 protocol to overwrite part of an object.

To overwrite part of an object, provide the data to be written and the starting offset. The data in the request is written starting at the provided offset. The format is: Range: <startingOffset>- .

For example, to write the data brown cat starting at offset 10, you issue this PUT request:

PUT /bucket1/object1 HTTP/1.1
Content-Length: 9
Range: bytes=10-
ACCEPT: application/json,application/xml,text/html,application/octet-stream
Date: Mon, 12 Mar 2018 20:51:41 -0000
x-emc-namespace: emc
Content-Type: application/octet-stream
Authorization: AWS wuser1:uwPjDAgmazCP5lu77Zvbo+CiT4Q=
Accept-Encoding: gzip, deflate, compress
 
brown cat
 
HTTP/1.1 204 No Content
ETag: 25
x-amz-id-2: object1
x-amz-request-id: 65be45c2-0ee8-448a-a5a0-fff82573aa3b
Content-Length: 0
Date: Mon, 12 Mar 2018 20:51:41 GMT

When the object is retrieved, part of the data is replaced at the provided starting offset (green fox is replaced with brown cat) and the final value is: The quick brown cat jumps over the lazy dog and cat.

GET /bucket1/object1 HTTP/1.1
Date: Mon, 12 Mar 2018 20:51:55 -0000
x-emc-namespace: emc
Content-Type: application/octet-stream
Authorization: AWS wuser1:/UQpdxNqZtyDkzGbK169GzhZmt4=
Accept-Encoding: gzip, deflate, compress
 
HTTP/1.1 200 OK
Date: Mon, 12 Mar 2018 20:51:55 GMT
Content-Type: application/octet-stream
Last-Modified: Mon, 12 Mar 2018 20:51:41 GMT
ETag: 25
Content-Type: application/json
Content-Length: 51
 
The quick brown cat jumps over the lazy dog and cat.

Note that when you overwrite existing parts of an object, the size and numbers of the new parts is added to the size and numbers of the existing parts you overwrote. For example, in a bucket that has one part that is 20 KB in size, you overwrite 5 KB. When you query the bucket using GET /object/billing/buckets/{namespace}/{bucketName}/info, the output will show total_mpu_size = 25 KB (not 20 KB) and total_mpu_parts = 2 (not 1) .