How much disk space is used?
The base install of FDSE uses 1.35 MB in 153 files. This includes program files, documents, and language files.
If necessary, you can immediately recover over half that space by deleting search/install, search/license, search/searchmods/powerusr, and any unused languages within search/searchdata/templates.
The search index file will be about half the combined size of all the HTML files that are indexed. The reduced size comes from stripping HTML tags, comments, extended whitespace, and common words. By default, FDSE will also only index the first 64kb of a file, ignoring the rest (see General Settings "Max Characters: File" and "Max Characters: Text" to control this).
For a site that contains 1000 6kb HTML files and 1000 20kb graphics, FDSE will ignore everything except the HTML files, and then use about 50% * 1000 files * 6 kb/file = 3 MB for the index. This is a very rough estimate. For text-intensive documents, the average size might be greater than 6kb, and the percentage of the file devoted to searchable text versus HTML tags will be greater than 50%.
When updating index files, FDSE uses a temp file which grows to the same size as the original file, so you will also need to have a bit of free space available during updates.
By default, each search is logged to searchdata/search.log.txt. Each record takes up about 70 bytes in the log. You can disable logging by going to "Admin Page" => "Usage Statistics" => "Logging: Enable" => "0" (unchecked).
"How much disk space is used?" http://www.xav.com/scripts/search/help/1140.html