I belive I have found a regression.

Inspired by 
<http://git-annex.branchable.com/forum/performance_improvement:_git_on_ssd__44___annex_on_spindle_disk/>
I tried to only have .git/annex/objects (also tested moving .git/annex) on NFS while having the rest on local SSD disk.

But when trying to add files i get:

     > git annex add testfile
    add testfile (checksum...) 
    git-annex: testfile: rename: unsupported operation (Invalid cross-device link)
    failed
    git-annex: add: 1 failed

I have tried both using bind-mount and with a sym-link.

> Grepping for `renameFile` and `createLink` will find all the places
> in git-annex that assume one filesystem. These would have to be changed
> to catch errors and fall back to expensive copying.
> 
> Putting a separate repository on the file server could work better
> depending on what you're trying to do. --[[Joey]] 

>> I've added support for putting `.git/annex` on a separate filesystem
>> from the rest of the git repository.
>> 
>> Putting individual subdirectories like `.git/annex/objects` on separate
>> filesystems from other subdirectories is not fully supported; it may
>> work but it may be slow and a few things (like `git annex migrate`) are
>> known to fail due to using hard links. I don't think this is worth
>> supporting. [[done]]
>> --[[Joey]]
