I have (i think?) noticed that the s3 remote doesn't really do an fsck:

http://source.git-annex.branchable.com/?p=source.git;a=blob;f=Remote/S3.hs;hb=HEAD#l86

Besides, unless S3 does something magic and amazingly fast, the checksum is just too slow for it to be really operational:

$ time git annex fsck -f s3 video/original/quartet_for_deafblind_h264kbs18000_24.mov
fsck video/original/quartet_for_deafblind_h264kbs18000_24.mov (checking s3...) ok
(recording state in git...)

real    0m1.188s
user    0m0.444s
sys     0m0.324s
$ time git annex fsck video/original/quartet_for_deafblind_h264kbs18000_24.mov
fsck video/original/quartet_for_deafblind_h264kbs18000_24.mov (checksum...)
ok
(recording state in git...)

real    3m14.478s
user    1m55.679s
sys     0m8.325s

1s is barely the time for git-annex to do an HTTP request to amazon, and what is returned doesn't seem to have a checksum of any kind:

fsck video/original/quartet_for_deafblind_h264kbs18000_24.mov (checking s3...) [2015-06-16 00:31:46 UTC] String to sign: "HEAD\n\n\nTue, 16 Jun 2015 00:31:46 GMT\n/isuma-files/SHA256E-s11855411701--ba268f1c401321db08d4cb149d73a51a10f02968687cb41f06051943b4720465.mov"
[2015-06-16 00:31:46 UTC] Host: "isuma-files.s3.amazonaws.com"
[2015-06-16 00:31:46 UTC] Response header 'x-amz-request-id': '9BF7B64EB5A619F3'
[2015-06-16 00:31:46 UTC] Response header 'x-amz-id-2': '84ZO7IZ0dqJeEghADjt7hTGKGqGAWwbwwaCFVft3ama+oDOVJrvpiFjqn8EY3Z0R'
[2015-06-16 00:31:46 UTC] Response header 'Content-Type': 'application/xml'
[2015-06-16 00:31:46 UTC] Response header 'Transfer-Encoding': 'chunked'
[2015-06-16 00:31:46 UTC] Response header 'Date': 'Tue, 16 Jun 2015 00:32:10 GMT'
[2015-06-16 00:31:46 UTC] Response header 'Server': 'AmazonS3'
[2015-06-16 00:31:46 UTC] Response metadata: S3: request ID=, x-amz-id-2=
ok

did i miss something? are there fsck checks for s3 remotes?

if not, i think it would be useful to leverage the "md5summing" functionality that the S3 API provides. there are two relevant stackoverflow responses here:

http://stackoverflow.com/questions/1775816/how-to-get-the-md5sum-of-a-file-on-amazons-s3 http://stackoverflow.com/questions/8618218/amazon-s3-checksum

... to paraphrase: when a file is PUT on S3, one can provide a Content-MD5 header that S3 will check against the uploaded file content for corruption, when doing the upload. then there is some talk about how the ETag header may hold the MD5, but that seems inconclusive. There's a specific API call for getting the MD5 sum:

https://docs.aws.amazon.com/AWSAndroidSDK/latest/javadoc/com/amazonaws/services/s3/model/ObjectMetadata.html#getContentMD5()

the android client also happens to check with that API on downloads:

https://github.com/aws/aws-sdk-android/blob/4de3a3146d66d9ab5684eb5e71d5a2cef9f4dec9/aws-android-sdk-s3/src/main/java/com/amazonaws/services/s3/AmazonS3Client.java#L1302

now of course MD5 is a pile of dung nowadays, but having that checksum beats not having any checksum at all. and it is at no cost on the client side... --anarcat