The UCSC Genome Browser hosts the following official mirror sites: the European mirror (genome-euro), located at the Universität Bielefeld Center for Biotechnology in Bielefeld, Germany and the Asian mirror (genome-asia), located at the RIKEN Yokohama Campus, Japan.

These mirror sites are administered by UCSC and are meant to be alternate, faster access points for those Browser users who are geographically closer to central Europe or Asia than to the western United States.

When users navigate to the U.S. server home page (and conversely, when U.S. users navigate to the European or Asian server) and click the "Genomes" menu item, they will receive a notification at the top of the window that they have been redirected to the more geographically-appropriate server. At this point, one of two things can happen:

1. The user may choose to remain on the redirected server and proceed normally.
2. The user may click the provided link back to the original server. When this occurs, a cookie is created in the user's Internet browser remembering this choice and in the future, no automatic redirection will occur.

The user may also manually select a server at any time by mousing over the "Mirrors" menu item, illustrated below. Note that manually selecting a server will also create a cookie that will disable automatic redirection. Automatic redirection can be re-enabled by clearing cookies.

Many thanks to our colleagues at the Universität Bielefeld Center for Biotechnology for hosting genome-euro, and at RIKEN for hosting genome-asia.

When genome-euro was first activated in 2013, the genome-euro Saved Sessions database was an identical copy of the Saved Sessions database from the U.S. server, so Saved Session data were the same on the two servers, except for custom tracks. After the initial activation of genome-euro, however, the Saved Sessions between the two servers began to diverge. New Saved Sessions or modifications to existing Saved Sessions are NOT copied from one server to the other, so a new Saved Session created on either server will NOT be available on the other. This is also the case on genome-asia (activated in 2016). Saved Sessions can be moved from one server to the other by saving them to a file and reloading the file using "Save current settings to a local file:" and "Use settings from a local file:" features on the Sessions page

Custom Track data, including those Custom Tracks belonging to Saved Sessions, are NOT copied from the U.S. server to mirror sites. Any Custom Tracks that exist on either the U.S. server or a mirror site will need to be manually downloaded via the Table Browser or otherwise manually recreated if users would like them to be present on the other.

Once Custom Tracks are loaded onto a mirror site, a Saved Session may be re-saved under the same name to reconstitute the original session with all associated Custom Tracks.

If you would like your custom data to be easily available on an official mirror site and the UCSC Genome Browser site, we highly recommend creating a Track Hub.

A track hub has the benefit of being hosted on your site allowing more control, ensuring data persistence, minimizing upload time to the browser, simplifying sharing of data, and optimizing track functionality.