Originally brought to my attention by Kate:
As a result of the changes to
XNAT-6424, when you delete a session in XNAT, you get a subdirectory under $cache/DELETED for every file in the session. For example, I deleted a session with 1 scan containing 160 files, and my DELETED folder ended up with 162 subdirectories (160 DICOM files, 1 XNAT log file, and 1 scan catalog XML). If you tried to delete sessions in a production environment, this would quickly get out of hand and crash performance on the file system pretty hard. For example, deleting 1 session with 100000 DICOM files would create over 100000 subdirectories directly under $cache/DELETED.