[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2015-06-16T17:50:56Z"
 content="""
You're incorrect; `git-annex fsck --from remote` works to fsck *any*
remote. For remotes like S3, it has to download the content to check it
locally, which is why `remoteFsck` is not provided.

Since you passed -f (--fast) to fsck, it avoids checksuming the content,
so avoids downloading it, and only verifies that S3 still says it has
the content. As documented on the git-annex fsck man page.

AFAICS, the Content-MD5 is only used by S3 to check that the data uploaded
to S3 didn't get corrupted over the wire. I assume that S3 implements its
own checksums to detect when data already stored on it gets corrupted, so
it seems redundant and complicating for git-annex to query it for md5sums.
It would work just as well for git-annex to verify a key after downloading
it, using the key's own hash, per [[todo/ checksum verification on transfer]].

It **might** be worth filling in the `poContentMD5` field with the md5 of
the file when uploading it to S3. Of course, this requires hashing the file
locally. And when storing an encrypted object on S3, it would require
buffering the whole encrypted object to disk first, in order to hash it
(but that's currently done anyway).
"""]]