Tip 37: Dedicated Crawl Servers in SharePoint 2010
This tip is for SharePoint Server 2010 and Search Server 2010 Express.
In the olden days MOSS 2007 😉 you could set a dedicated web front end for crawling which is used to reduce the stress of crawling from other web front end servers that users use to browse.
This setting is for the entire search service, so all local SharePoint sites will use the dedicated web front end server.
In SharePoint Server 2010 you can still set a dedicated web front end for crawling but there are some changes. First the setting is not search service wide, it is a web application setting. Second, as of this time, there is no UI to change the web application settings for dedicated crawls. To set a web application to crawl with a dedicated web front end you will need to use PowerShell. The link above has some examples of PowerShell to add a dedicated web front end and to remove a web front end. To list if a web application is using dedicated web front end settings use the example below, if any values are returned, then the web application has dedicate web front end settings. Otherwise the output will be empty (SiteDataServers : {}).
$WebApplication=Get-SPWebApplication http://www.contoso.com
$WebApplication|fl SiteDataServers