How do I let my readers search my entire blog?or
Why does my Search not find all of my posts?Both of these questions - and more - are seen, because not every blog owner is aware of the limitations, and possibilities, of each search technique.
Look at the top of the sidebar, in this blog.
See "Search Me, Direct" and "Search Me, Custom"? That's two gadgets, with a common goal - help you, my reader, find information in this blog. And each gadget works just slightly differently.
The Custom Search.
A "custom" - or "indexed" - search works from search engine cache. All blog content, as indexed, can be retrieved in a custom search.
A custom search lets you display content outside the blog being displayed - and it does that with the blog page, that you are reading, still on screen. This makes it good for contextual searches.
A custom search won't work so well for new blogs, for blogs just renamed or published to a custom domain, for empty or "test" blogs, or for blogs that have a problem with search engine indexing in general. For any of these cases, you should consider providing a direct search gadget - at least, as an alternative.
The Direct Search.
A "direct" search works from published blog content. All posts content, immediately when published, can be retrieved in a direct search.
A direct search lets you display the posts as entries in an index page - just as you would view an archive retrieval or label search. It looks more like blog content, simply in a different context.
A direct search will only retrieve content published in a post. Static pages won't appear in a direct search, even if they are indexed. Nor will content displayed in a gadget be retrieved. For any of these cases, you should consider providing a custom search gadget - at least, as an alternative.
The bottom line.
Neither gadget will replace the other - all of the time, and for all retrieval needs. A well equipped blog may need both searches, as a portion of a properly planned dynamic retrieval strategy.