Yup. Also fails if you don't have write access or disk is full or out of inodes or...

Short version: I think in that case we should be erroring out and letting the admin running it deal with it rather than (attempting to!) creating directories.

Perhaps a check the directory exists on startup might be appropriate however - a persistormanager.validate call? I seem to remember there being a check in there somewhere that the s3 keys were set, so possibly could abstract that in for the s3 manager?