Over the past year, I have had a couple of problems with hosting providers for a few of our sites.   It happens ? and to be fair, sometimes it is out of the hands of the hosting provider when hard drives fail or servers crash (in fact recently Google has released a report on the hard drive failures in their data centres with an average failure rate of 8-10% from hard drives at least 2 years old).  But it is the speed in resolving these issues that will prevent a negative impact on your search engine rankings.

If GoogleBot arrives at your site and it is not there it will give you the benefit of the doubt and will try again later.. but after ?a few? visits and your site is still not available then you will actually be dropped from the index.  Which as you can imagine ? could be disastrous for your business.

Here?s what Vanessa Fox from Google said about this subject in a recent Google Groups thread:

If the host is down when Googlebot tries to access your pages, then those pages may disappear from the index until Googlebot can crawl them again. In webmaster tools, do the pages you want indexed appear in the crawl errors section? If so, then Googlebot was unable to access them.

If you are moving the site to a new host and the pages are available the next time Googlebot tries to access them, then you should see them in the index again soon after that.

So as you can see ? if your site goes down and if it is not resolved quickly, then you will actually be removed from the index completely.  When your site is back up, you will be re-included, but there are no guarantees on how long that will take or if you will rankings will be returned to their pre-crash state.

And so my advice to you is to ensure that you work with a hosting provider that has a solid track record and some sort of guarantees of up-time.  You should also consider subscribing to a site monitoring service to make sure that you are notified if your site is down.

If your site does go down, make sure that you resolve the issue quickly (even if it means redirecting to a secondary server temporarily like we had to do last year) to protect your rankings.