Sitemap Output
Each time the sitemap generation job is executed, the result is one index file (sitemap_index.xml) and one or more actual sitemap files (sitemap_0.xml, sitemap_1.xml, ...).
The index file is the file that you register with the search engine. Its only purpose is to point to the actual sitemaps. The actual number of sitemap files is determined by the configurable of URLs per sitemap file (for example, 50,000) or by a maximum size of 10 MB per sitemap file, whichever condition is reached first.
Sitemap Output Locations
Your sitemap must be located on your production system for Google to index the production system.
To view the index file, point your browser to the following URL:
http://<hostname>/sitemap_index.xml
The index file includes the locations of all sitemap files. If you have difficulty seeing the sitemap_index.xml file, make sure that you are using a hostname set in the hostname alias. Also make sure that you are including the full hostname and not simply the store name.