Data Management

The data volume is driven by the total number of fields times the number of exposures times the filters per field divided by the field size of the CCD. In a single filter, and during optimal time in the year, we can do the entire PLATO FOV within one night. If the optional two-filter mode is decided, then at most 30 of the needed 60 BMK10k pointings can be done in one night.
Therefore, our default is a single-filter operation at the time being. Then, we can afford a (field) overlapping factor of nearly 30%. With a total of 60 pointings by BMK10k, and three exposures per pointing (200s, 60s, and 10s), and additionally ≈50 calibration images per night during twilight, the nightly data rate sums up to approximately 230 CCD frames for an “ideal” night and takes approximately 8 hours. Each frame requires a disk space of 223 MB and we thus expect ≈50 GB per night at maximum. The full visibility season of the long-pointing field is approximately 1300 hours (Fig. 12a) and the expected data volume per observing season is then at most ≈9 TB without compression given the expected “open roof” probability in Fig. 12b.

Two-times lossless compression makes this a data-generation rate of at most ≈1.8 MB/s for 1300 hours. This is thus the minimum bandwidth required for continuous data transfer. The entire data-transportation chain consists of the transfer

  1. from the CCD controller’s computers to the main site computer,
  2. from the main site computer’s RAID array(s) to a tape station and,
  3. from the RAID array via internet to the MCC home computer in Potsdam.

Above average data rate appears no problem for a standard 100Base TX ethernet link for transfer a). Transfer b) will require a tape stations in parallel in order to tape the data in real time, if desired (tbd). Current products, e.g. HP Storageworks Ultrium 960 SCSI, suggest writing speeds of 80 MB/s for 400GB SDLTs though. Higher compression factors for storage and transfer are also possible.

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