I just noticed this option under in Library Maintenance so tried it to see what happened. This was the result:
Spoiler:
calibre, version 0.8.43
ERROR: Unhandled exception: <b>DatabaseException</b>:disk I/O error
RemoteTraceback (most recent call last):
File "site-packages\calibre\library\sqlite.py", line 271, in run
OperationalError: disk I/O error
Traceback (most recent call last):
File "site-packages\calibre\gui2\actions\choose_library.py", line 374, in check_library
File "site-packages\calibre\gui2\ui.py", line 536, in library_moved
File "site-packages\calibre\gui2\tag_browser\view.py", line 143, in set_database
File "site-packages\calibre\gui2\tag_browser\model.py", line 258, in set_database
File "site-packages\calibre\library\prefs.py", line 58, in set
File "site-packages\calibre\library\prefs.py", line 54, in __setitem__
File "site-packages\calibre\library\sqlite.py", line 314, in run
DatabaseException: disk I/O error
RemoteTraceback (most recent call last):
File "site-packages\calibre\library\sqlite.py", line 271, in run
OperationalError: disk I/O error
Would some kind person please explain what this means?