Please describe the problem.

After unlocking a repository, the next git status will take time linear to the file size. It seems to be highly inefficient (the I/O on my SSD is not anywhere near the limit).
For a 500Mb flac album it takes ~5–10s, for my 100GB local music archive it took well over 30min.

What steps will reproduce the problem?

git annex upgrade
git annex unlock
git status / git add -A

What version of git-annex are you using? On what operating system?

6.20160527
NixOS (master branch)

Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Not yet. :)
But will use it to keep my music library and sync a smaller (ogg) version to my various devices (with beets handling metadata and conversion)