I have files with very long filenames on an xfs at home. On my laptop the annex should have been checked out on an encfs, but there filenames can't be as long as on the xfs. So perhaps it would be good to limit the keysize to a sane substring of the filename e.g. use only the first 120 characters.
Since there seems no strong argument for a WORM100, and better options exist, closing. done --Joey
Seems like you probably have files in git with nearly as long filenames as the key files. Course, you can rename those yourself.
This couldn't be changed directly in WORM without some ugly transition, but it would be possible to implement it as a WORM100 or so. OTOH, if you're going to git annex migrate, you might as well use SHA1.
I wouldn't say it's completly impossible for a WORM100 to work. It would just have the contract that the pair of mtime+100chars has to be unique for each unique piece of data.
But, I have yet to be convinced there's any point, since SHA1 exists.