1. Introduction What purpose does a data archive center serve if users can’t find or access the holdings they might need to facilitate their research discoveries? Removing the barriers that prevent discovery and access of data assets, by a diverse set of users, is a ongoing challenge facing data archive centers today. To manage this challenge, The NCAR Research Data Archive (RDA) employs a combination of in-house developed and standards based community discovery and access tools which support more than 10,000 users annually. The tools and user communities they serve are highlighted in this presentation. Workers remove a road closed barrier as a new bridge opens. Image courtesy “www.readthehook.com” System Design The RDA provides a variety of search, discovery, and access tools to serve a broad user community (Figure 1). Distributed searches and metadata harvesting are supported by an Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) access point, and a Geoportal server with a Catalog Services for the Web (CSW) access point. The in-house developed web interface provides keyword and faceted search options, and access to detailed dataset metadata. Once users find the data they want, several options are available to support data access. Data subset requests can be submitted through web interfaces, command line app clients, command line apps located on internal HPC systems, and Unidata THREDDS catalog supported web protocols. Data files and resulting subset request output files can be downloaded by server generated Wget and cURL scripts, or through the command line app clients. Acknowledgments The members of the NCAR Computational Inforamtion Systems Laboratory (CISL), Data Support Section (DSS) support the infrastructure and software described in this presentation. They include Joey Comeaux, Thomas Cram, Cecilia Banner, Bob Dattore, Zaihua Ji, Kevin Manross, Dave Stepaniak, and Chi-Fan Shih. Figure 1. RDA Data Discovery and Access System Usage Metrics User metrics display a continued growth in use of customized request access options (Figure 2), and fairly steady use of direct archive file downloads through the web interface (Figure 3). Figure 2. Monthly customized RDA user access from the web interface. Access options include data subset and file format conversion requests. Figure 3. Monthly RDA direct archive file download from the web interface. Wget and cURL download scripts drive this usage. Partial file downloads of user selected parameters are supported by the cURL based scripts. Once sufficient data are available, usage metrics will also be compiled for the THREDDS and command line apps/app clients data access methods. Douglas Schuster and Steven Worley CISL/DSS, National Center for Atmospheric Research, Boulder, CO, United States.,, http://rda.ucar.edu Relevant Links RDA Geoportal instance http://rda.ucar.edu/geoportal RDA Geoportal CSW endpoint http://rda.ucar.edu/geoportal/csw/discovery?Request=GetCapabilitie s&Service=CSW&Version=2.0.2 RDA OAI-PMH endpoint http://rda.ucar.edu/cgi-bin/oai RDA THREDDS data server http://rda.ucar.edu/thredds/catalog.html RDA command line app clients http://rda.ucar.edu/#apps RDA HTTP PHP API description http://rda.ucar.edu/#apps_api_desc The NCAR Research Data Archive’s Hybrid Approach for Data Discovery and Access Currently/Month 1 PB Data Processed 30 TB Data Delivered 3000 Requests 500 Users Currently/Month 75 TB Data Accessed 40 TB Data Delivered 1500 Users