The Submillimeter Array (SMA) is under construction at Mauna Kea (Moran 1998). The SMA's first fringes from observations of celestial sources were obtained with two antennae on September 29, 1999. A year later, the first phase closures were successfully achieved on Uranus. A synthesis image of this planet at 230GHz was made from the observations using the SMA's first three elements. As the SMA correlator comes on-line, the maximum data production rate will approach 2.75MB per sampling. For a typical integration time of 10 seconds, the daily data production rate of the SMA would be 20GB/day. In this paper, we present the design of the data-handling system and report the status of the software development in support of data reduction and analysis for SMA users.
Figure 1 shows an overview of the architecture of the SMA on-line data-handling software. Communication between the data-handling computer Smadata (a Sun Ultra 60 running Solaris) and the real-time system (the SMA correlator Crates and a control computer Hal9000) is accomplished with remote procedure calls (RPC) via a local network (100 Meg/sec Ethernet). Smadata is a central host of the data-handling server (smadata-svc), performing the post-correlator data processes such as data formatting, on-line correction, and flagging. In addition, this data computer also hosts the servers for data archiving, database management, data replication and HTTP.
The RPC server smadata_svc, developed in C, provides several data services to process the data received from real-time computers Crates and Hal9000. The cross-correlation data from the SMA correlator and ancillary data are organized and stored in a number of FITS tables following the FITS-IDI standard (Diamond et al. 1997;Flatters 1998). During an observing run, a visibility data monitor (Vis_monitor, under development in AIPS++) will provide a handy, run-time imaging facility for data quality control. At the end of each observing run, a single portable FITS-IDI is produced. The SMA FITS-IDI can be directly read into the AIPS environment and is ready for off-line data analysis.
With this commercial software, we are also developing an on-line archive system to handle SMA interferometer data. The FITS-IDI files will be stored in mass storage. The header information of the FITS tables in each FITS-IDI file along with the file location is archived in the SMA astronomical database (SMADB), which is managed by the Sybase server. The preliminary design of this system is illustrated in Figure 1. At the termination of each observing run, the RPC server smadata_svc triggers a process, FITStoDB, which extracts all the header data from the FITS-IDI files and converts them to the database in Sybase.
A JDBC driver, Sybase's jConnect, has been installed in the Server host computer Smadata. The basic configuration for the SMA On-Line Archive System is illustrated in Figure 1. JDBC provides standard Java API codes that allow us to develop a specific Java Applet GUI (Graphical User Interface) to communicate with SMADB via the SQL server. The data computer also hosts an HTTP server. This Server provides a port for outside clients to download Java Applets and therefore to establish a connection with the database server. As soon as the client/server connection is established, the data transaction can proceed via the network.
We continue to investigate hardware devices for data storage, including a DLT library or DVD-R juke-box. However, we have a temporary solution for keeping the visibility data on-line during the construction and testing phase. The current storage hardware system is implemented with several multipack disks attached to the data server Smadata (Ultra 60) while either the DLT library or DVD-R juke box is being considered.
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Zhao, J.-H., Mailhot, P., and Tsutsumi, T., 2000, SMA Technical Memo No. 138 (SAO)