When building an index and the disk fills up, no error is reported.
I used

swish-e -S fs -i Articles

to build an index, but didn't know the disk was too full for two
copies (the current one and the one being built) of the index.
Subsequent lookups using the truncated index returned no matches, and
no indication that the index was bad either.  Some additional error
checking and reporting would be helpful...