HD (compressed & uncompressed) and Computer (Capture & RAID) Bandwidths

I like to have a feel for bandwidths – roughly how big these things are and why.  Especially when I start running out of storage space and having to purchase additional disk drives etc…   Also I like to get a handle on how adequate my RAID will be for capturing uncompressed HD.  Google-search & calculations:

  • In the case of HD-SDI (1080i50), bitrate is around 1.5 Gbps [http://www.filmmakermagazine.com/fall2006/line_items/hdmi.php]
  • In our case we have 720p50, but that apparently has about the same uncompressed bandwidth as 1080i50, namely 1.5Gbps [http://www.dtvforum.info/index.php?showtopic=9100]
  • My system has a RocketRaid+ProAVIO RAID5 arrangement.  I have not yet tested its uncompressed capture ability (I havea BlackMagic card), but it (if I’ve calculated it right), it looks like it should handle it easily.
    • RocketRaid themselves report tests [http://www.highpoint-tech.com/PDF/RR2522/RR2522_Performance_Report.pdf] involving an AJA capture card and a RAID5 array (as is mine) giving read and write speeds at about 400MBps (=3.2Gbps, because B i.e. Bytes = 8*b = Bits). 
      • If I understand this right, my system has a capture bandwidth twice that an uncompressed HD signal.  Plenty of headroom then.
  • ProRes’s 123 Mbps is not far off the “100Mbps” figure often mentioned in relation to the Convergent Design flash memory recorder, at which level the recording, compressed (as is ProRes) in a variant of MPEG2, is regarded as almost indistinguishable from uncompressed.

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