At current state, attachments in JIRA are stored inside attachments/project-name, in the hierarchy below:

- attachments
 |- project-name
   |- issue key

Since attachments are associated with issue keys, this could pose a problem for those on a Linux/UNIX platform. The ext3 filesystem can only have a maximum of 32,000 subdirectories per directory. The ext4 filesystem has fixed this limitation and increase its size to 64,000 subdirectories per directory.

The problem creeps in when you have 65,000 issues per project. If this was the case, then JIRA would not be able to save any more attachments and this would be problematic.