Attachments, when stored on the file system, are stored in this format:

<confluence-home>/Attachments/<PageID>/<AttachmentID>/<AttachmentVersion>

If there are more than 31,999 pages with attachments, some OS limits will be exceeded, resulting in errors when trying to create the 32,000th directory under the Attachments folder.

Directories are created in the Attachments folder when an attachment is first added to a page. As an improvement, they could be deleted when attachments are deleted from a page. A larger scale correction for this issue would be to add another directory such as Space ID as a top level.